Thin film magnetic memory device including memory cells having a magnetic tunnel junction

ABSTRACT

In the data read operation, a memory cell and a dummy memory cell are respectively coupled to two bit lines of a selected bit line pair, and a data read current is supplied thereto. In the selected memory cell column, a read gate drives the respective voltages on a read data bus pair, according to the respective voltages on the bit lines. A data read circuit amplifies the voltage difference between the read data buses so as to output read data. The use of the read gate enables the read data buses to be disconnected from a data read current path. As a result, respective voltage changes on the bit lines are rapidly produced, whereby the data read speed can be increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film magnetic memory device.More particularly, the present invention relates to a random accessmemory (RAM) including memory cells having a magnetic tunnel junction(MTJ).

2. Description of the Background Art

An MRAM (Magnetic Random Access Memory) device has attracted attentionas a memory device capable of non-volatile data storage with low powerconsumption. The MRAM device is a memory device that stores data in anon-volatile manner using a plurality of thin film magnetic elementsformed in a semiconductor integrated circuit and is capable of randomaccess to each thin film magnetic element.

In particular, recent announcement shows that significant progress inperformance of the MRAM device is achieved by using thin film magneticelements having a magnetic tunnel junction (MTJ) as memory cells. TheMRAM device including memory cells having a magnetic tunnel junction isdisclosed in technical documents such as ∓A ions Read and WriteNon-Volatile Memory Array Using a Magnetic Tunnel Junction and FETSwitch in each Cell”, ISSCC Digest of Technical Papers, TA7.2, February2000, and “Nonvolatile RAM based on Magnetic Tunnel Junction Elements”,ISSCC Digest of Technical Papers, TA7.3, February 2000.

FIG. 83 is a schematic diagram showing the structure of a memory cellhaving a magnetic tunnel junction (hereinafter, also simply referred toas “MTJ memory cell”).

Referring to FIG. 83, the MTJ memory cell includes a magnetic tunneljunction MTJ whose resistance value varies according to the storage datalevel, and an access transistor ATR. The access transistor ATR is formedfrom a field effect transistor, and is coupled between the magnetictunnel junction MTJ and the ground voltage Vss.

For the MTJ memory cell are provided a write word line WWL forinstructing a data write operation, a read word line RWL for instructinga data read operation, and a bit line BL serving as a data line fortransmitting an electric signal corresponding to the storage data levelin the data read and write operations.

FIG. 84 is a conceptual diagram illustrating the data read operationfrom the MTJ memory cell.

Referring to FIG. 84, the magnetic tunnel junction MTJ has a magneticlayer FL having a fixed magnetic field of a fixed direction(hereinafter, also simply referred to as “fixed magnetic layer FL”), anda magnetic layer VL having a free magnetic field (hereinafter, alsosimply referred to as “free magnetic layer VL”). A tunnel barrier TBformed from an insulator film is provided between the fixed magneticlayer FL and the free magnetic layer VL. According to the storage datalevel, either a magnetic field of the same direction as that of thefixed magnetic layer FL or a magnetic field of the direction differentfrom that of the fixed magnetic layer FL has been written to the freemagnetic layer VL in a non-volatile manner.

In reading the data, the access transistor ATR is turned ON in responseto activation of the read word line RWL. As a result, a sense current Isflows through a current path formed by the bit line BL, magnetic tunneljunction MTJ, access transistor ATR and ground voltage Vss. The sensecurrent Is is supplied as a constant current from a not-shown controlcircuit.

The resistance value of the magnetic tunnel junction MTJ variesaccording to the relative relation of the magnetic field directionbetween the fixed magnetic layer FL and the free magnetic layer VL. Morespecifically, in the case where the fixed magnetic layer FL and the freemagnetic layer VL have the same magnetic field direction, the magnetictunnel junction MTJ has a smaller resistance value as compared to thecase where both magnetic layers have different magnetic fielddirections.

Accordingly, in the data read operation, a voltage change produced atthe magnetic tunnel junction MTJ due to the sense current Is variesaccording to the magnetic field direction stored in the free magneticlayer VL. Thus, by starting supply of the sense current Is with the bitline BL precharged to a high voltage, the storage data level in the MTJmemory cell can be read by monitoring a voltage level change on the bitline BL.

FIG. 85 is a conceptual diagram illustrating the data write operation tothe MTJ memory cell.

Referring to FIG. 85, in the data write operation, the read word lineRWL is inactivated, and the access transistor ATR is turned OFF. In thisstate, a data write current for writing a magnetic field to the freemagnetic layer VL is applied to the write word line WWL and the bit lineBL. The magnetic field direction of the free magnetic layer VL isdetermined by combination of the respective directions of the data writecurrent flowing through the write word line WWL and the bit line BL.

FIG. 86 is a conceptual diagram illustrating the relation between therespective directions of the data write current and the magnetic fieldin the data write operation.

Referring to FIG. 86, a magnetic field Hx of the abscissa indicates thedirection of a magnetic field H(WWL) produced by the data write currentflowing through the write word line WWL. A magnetic field Hy of theordinate indicates the direction of a magnetic field H(BL) produced bythe data write current flowing through the bit line BL.

The magnetic field direction stored in the free magnetic layer VL isupdated only when the sum of the magnetic fields H(WWL) and H(BL)reaches the region outside the asteroid characteristic line shown in thefigure. In other words, the magnetic field direction stored in the freemagnetic layer VL is not updated when a magnetic field corresponding tothe region inside the asteroid characteristic line is applied.

Accordingly, in order to update the storage data of the magnetic tunneljunction MTJ by the data write operation, a current must be applied toboth the write word line WWL and the bit line BL. Once the magneticfield direction, i.e., the storage data, is stored in the magnetictunnel junction MTJ, it is held therein in a non-volatile manner until anew data write operation is conducted.

The sense current Is flows through the bit line BL in the data readoperation. However, the sense current Is is generally set to a valuethat is smaller than the above-mentioned data write current by about oneor two orders of magnitude. Therefore, it is less likely that thestorage data in the MTJ memory cell is erroneously rewritten during thedata read operation due to the sense current Is.

The above-mentioned technical documents disclose a technology of formingan MRAM device, a random access memory, having such MTJ memory cellsintegrated on a semiconductor substrate.

FIG. 87 is a conceptual diagram showing the MTJ memory cells arranged inrows and columns in an integrated-manner.

Referring to FIG. 87, with the MTJ memory cells arranged in rows andcolumns on the semiconductor substrate, a highly integrated MRAM devicecan be realized. FIG. 87 shows the MTJ memory cells arranged in n rowsby m columns (where n, m is a natural number).

As described before, the bit line BL, write word line WWL and read wordline RWL must be provided for each MTJ memory cell. Accordingly, n writeword lines WWL1 to WWLn, n read word lines RWL1 to RWLn, and m bit linesBL1 to BLm are required for the n×m MTJ memory cells.

Thus, the MTJ memory cells are generally provided with the independentword lines for the read and write operations.

FIG. 88 is a structural diagram of the MTJ memory cell provided on thesemiconductor substrate.

Referring to FIG. 88, the access transistor ATR is formed in a p-typeregion PAR of the semiconductor main substrate SUB. The accesstransistor ATR has source/drain regions (n-type regions) 110, 120 and agate 130. The source/drain region 110 is coupled to the ground voltageVss through a metal wiring formed in a first metal wiling layer M1. Ametal wiring formed in a second metal wiring layer M2 is used as thewrite word line WWL. The bit line BL is provided in a third metal wiringlayer M3.

The magnetic tunnel junction MTJ is provided between the second metalwiling layer M2 of the write word line WWL and the third metal wilinglayer M3 of the bit line BL. The source/drain region 120 of the accesstransistor ATR is electrically coupled to the magnetic tunnel junctionMTJ through a metal film 150 formed in a contact hole, the first andsecond metal wiling layers M1 and M2, and a barrier metal 140. Thebarrier metal 140 is a buffer material for providing electrical couplingbetween the magnetic tunnel junction MTJ and the metal wirings.

As described before, the MTJ memory cell is provided with the read wordline RWL independently of the write word line WWL. In addition, in thedata write operation, a data write current for generating a magneticfield equal to or higher than a predetermined value must be applied tothe write word line WWL and the bit line BL. Accordingly, the bit lineBL and the write word line WWL are each formed from a metal wiling.

On the other hand, the read word line RWL is provided in order tocontrol the gate voltage of the access transistor ATR, and a currentneed not be actively applied to the read word line RWL. Accordingly,from the standpoint of the improved integration degree, the read wordline RWL is conventionally formed from a polysilicon layer, polycidestructure, or the like in the same wiring layer as that of the gate 130without providing an additional independent metal wiring layer.

As described in connection with FIG. 84, the data read operation of theMTJ memory cell is conducted based on the voltage change caused by thesense current (Is in FIG. 84) supplied to the magnetic tunnel junctionMTJ serving as a resistive element. This voltage change cannot bequickly produced with a large RC (resistance-capacitance) time constantof the sense current path, making it impossible to increase the dataread operation speed.

Moreover, as shown in FIG. 86, the data write operation is conductedbased on the relation between the applied magnetic field and theasteroid characteristic line provided as a threshold. Accordingly,variation in asteroid characteristic line as produced in manufacturingthe memory cells results in variation in data write margin to the memorycell.

FIG. 89 is a conceptual diagram illustrating the effects of themanufacturing variation on the data write margin.

Referring to FIG. 89, the design value of the asteroid characteristicline is denoted with ASd. It is now assumed that the asteroidcharacteristic line of the memory cell is deviated from the designvalue, as shown by ASa or ASb.

For example, in the MTJ memory cell having the asteroid characteristicline ASb, the data cannot be written even if the data write currentaccording to the design value is supplied for application of the datawrite magnetic field.

On the other hand, in the MTJ memory cell having the asteroidcharacteristic line ASa, the data is written even if the data writemagnetic field smaller than the design value is applied. As a result,the MTJ memory cell having such characteristics is extremely susceptibleto the magnetic noise.

Such manufacturing variation in asteroid characteristic line may furtherbe increased as the memory cells are miniaturized for improvedintegration. Accordingly, in order to ensure the manufacturing yield,there is a need not only for development of the manufacturing technologythat reduces the manufacturing variation in asteroid characteristicline, but also for the adjustment technology for ensuring an appropriatedata write margin corresponding to the variation in asteroidcharacteristic line.

Moreover, as described in connection with FIGS. 85 and 86, a relativelylarge data write current must be supplied to the bit line BL and thewrite word line WWL in the data write operation. As the data writecurrent is increased, the current density in the bit line BL and thewrite word line WWL is also increased, which may possibly cause aphenomenon called electromigration.

Electromigration may cause disconnection or short-circuit of thewirings, thereby possibly degrading the operation reliability of theMRAM device. Moreover, an increased data write current may possiblyproduce a considerable amount of magnetic noise. It is thereforedesirable to realize the structure capable of writing the data with asmaller data write current.

As described in connection with FIGS. 87 and 88, a large number ofwirings are required to write and read the data to and from the MTJmemory cell, making it difficult to reduce the area of the memory arrayintegrating the MTJ memory cells, and thus the chip area of the MRAMdevice.

An MTJ memory cell using a PN junction diode as an access elementinstead of the access transistor is known as a memory cell structurecapable of achieving improved integration over the MTJ memory cell shownin FIG. 83.

FIG. 90 is a schematic diagram showing the structure of the MTJ memorycell using the diode.

Referring to FIG. 90, the MTJ memory cell using the diode includes amagnetic tunnel junction MTJ and an access diode DM. The access diode DMis coupled between the magnetic tunnel junction MTJ and the word lineWL. Herein, the direction from the magnetic tunnel junction MTJ towardthe word line WL is the forward direction. The bit line BL extending insuch a direction that crosses the word line WL is coupled to themagnetic tunnel junction MTJ.

In the MTJ memory cell using the diode, the data write operation isconducted with the data write current being supplied to the word line WLand the bit line BL. As in the case of the memory cell using the accesstransistor, the direction of the data write current is set according tothe write data level.

On the other hand, in the data read operation, the word line WLcorresponding to the selected memory cell is set to the low voltage(e.g., ground voltage Vss) state. By precharging the bit line BL to thehigh voltage (e.g., power supply voltage Vcc) state, the access diode DMis rendered conductive, allowing the sense current Is to be suppliedthrough the magnetic tunnel junction MTJ. The word lines WLcorresponding to the non-selected memory cells are set to the highvoltage state. Therefore, the corresponding access diodes DM areretained in the OFF state, and no -sense current Is flows therethrough.

Thus, the data read and write operations can be conducted also in theMTJ memory cell using the access diode.

FIG. 91 is a structural diagram of the MTJ memory cell of FIG. 90provided on the semiconductor substrate.

Referring to FIG. 91, the access diode DM is formed on the semiconductorsubstrate SUB from an N-type region NWL formed from, e.g., an N-typewell, and a P-type region PRA formed thereon.

The N-type well NWL, which corresponds to the cathode of the accessdiode DM, is coupled to the word line WL provided in the metal wilinglayer M1. The P-type region PRA, which corresponds to the anode of theaccess diode DM, is electrically coupled to the magnetic tunnel junctionMTJ through the barrier metal 140 and the metal film 150. The bit lineBL is provided in the metal wiling layer M2 so as to be coupled to themagnetic tunnel junction MTJ. Thus, by replacing the access transistorwith the access diode, the MTJ memory cell that is advantageous in termsof improvement in integration degree can be obtained.

The data write current flows through the word line WL and the bit lineBL in the data write operation. This causes a voltage drop on theselines. Such a voltage drop may turn ON the PN junction of the accessdiode DM of at least one of the MTJ memory cells that are not selectedfor the data write operation. As a result, a current may unexpectedlyflow through the MTJ memory cell, causing an erroneous data writeoperation.

Thus, the conventional MTJ memory cell using the access diode isadvantageous in terms of improved integration, but is problematic inview of the stability of the data write operation.

SUMMARY OF THE INVENTION

It is an object of the present invention to increase the data writespeed in an MRAM device including MTJ memory cells.

It is another object of the present invention to provide the structurecapable of easily adjusting the amount of data write current so as toassure a predetermined data write margin in the MRAM device includingthe MTJ memory cells, by compensating for variation in magneticcharacteristics due to manufacturing variation.

It is a further object of the present invention to achieve improvementin operation reliability as well as suppression of magnetic noise in theMRAM device including the MTJ memory cells, by reducing the data writecurrent.

It is a still further object of the present invention to provide the MTJmemory cell structure capable of improved integration and providingexcellent operation reliability.

It is a yet further object of the present invention to suppress the chiparea of the MRAM device including the MTJ memory cells arranged in anarray, by improving the freedom of layout as well as reducing the numberof wirings required for the entire memory array.

In summary, according to the present invention, a thin film magneticmemory device includes a memory array, a plurality of first bit lines, aplurality of read word lines, a first read data line, a read gatecircuit, and a data read circuit. The memory array includes a pluralityof magnetic memory cells arranged in rows and columns. Each of theplurality of magnetic memory cells has either a first or secondresistance value according a storage data level thereof. The pluralityof first bit lines are provided corresponding to the respective columnsof the magnetic memory cells. The plurality of read word lines areprovided corresponding to the respective rows of the magnetic memorycells, for electrically coupling the magnetic memory cells correspondingto an addressed row between the plurality of first bit lines set to afirst voltage and a second voltage (Vss), respectively, so as to pass adata read current through the magnetic memory cells. The first read dataline transmits read data. The read gate circuit sets a voltage of thefirst read data line according to a voltage on one of the plurality offirst bit lines that corresponds to an addressed column. The data readcircuit sets a level of the read data according to the voltage on thefirst read data line.

Therefore, a primary advantage of the present invention is that the dataread speed can be increased by rapidly producing a voltage change on thefirst bit line by conducting the data read operation with a reduced RCconstant of the data read current path, without supplying any data readcurrent to the first read data line.

According to another aspect of the present invention, a thin filmmagnetic memory device having a normal operation mode and a test modeincludes a memory array, a plurality of write word lines, a write wordline driver, a data write circuit, and a plurality of bit line pairs.The memory array includes a plurality of magnetic memory cells arrangedin rows and columns. Each of the plurality of magnetic memory cells hasa different resistance value according to a level of storage datawritten when a data write magnetic field applied by first and seconddata write currents is larger than a predetermined magnetic field. Theplurality of write word lines are provided corresponding to therespective rows of the magnetic memory cells, and selectively activatedaccording a row selection result in a data write operation. The writeword line driver supplies the first data write current to the activatedword line in an amount corresponding to a voltage level on a firstcontrol node. The data write circuit supplies the second data writecurrent in the data write operation in an amount corresponding to avoltage level on a second control node. The plurality of bit lines areprovided corresponding to the respective columns of the magnetic memorycells, and selectively connected to the data write circuit according toa column selection result in the data write operation. At least one ofthe write word line driver and the data write circuit includes an inputterminal for externally setting the voltage level of a corresponding oneof the first and second control nodes in the test mode.

Accordingly, in the test mode, at least one of the first and second datawrite currents can be set from the outside. Thus, the manufacturingvariation in magnetic characteristics of the MTJ memory cells can becompensated for, whereby the adjustment testing of the data writecurrent amount for appropriately ensuring a data write margin can befacilitated.

According to a further aspect of the present invention, a thin filmmagnetic memory device includes a memory array, a plurality of bitlines, a plurality of write word lines, and a coupling circuit. Thememory array includes a plurality of magnetic memory cells arranged inrows and columns. Each of the plurality of magnetic memory cellsincludes a magnetic storage portion having a different resistance valueaccording to a level of storage data written when a data write magneticfield applied by first and second data write currents is larger than apredetermined magnetic field. The plurality of bit lines are providedcorresponding to the respective columns of the magnetic memory cells,for passing the first data write current therethrough. The plurality ofwrite word lines are provided corresponding to the respective rows ofthe magnetic memory cells, and selectively activated according anaddress selection result so as to pass the second data write currenttherethrough in a data write operation. Each of the write word linesincludes first and second sub write word lines respectively formed infirst and second metal wiring layers with the magnetic storage portionsinterposed therebetween in a vertical direction on a semiconductorsubstrate. The coupling circuit electrically couples the first andsecond sub write word lines to each other. The second data write currentflows as a reciprocating current through the first and second sub writeword lines electrically coupled to each other by the coupling circuit.

Thus, since the data write current flows as a reciprocating currentthrough the first and second bit lines that are electrically coupled toeach other, data write magnetic fields acting in the same direction canbe generated in the magnetic storage portion. This reduces the amount ofdata write current required to generate a data write magnetic field ofthe same strength. As a result, reduced power consumption of the MRAMdevice, improved operation reliability resulting from the reducedcurrent density of the bit line, and also reduced magnetic field noisein the data write operation can be realized.

According to a still further aspect of the present invention, a thinfilm magnetic memory device includes a memory array, a plurality of readword lines, a plurality of write word lines, and a plurality of bitlines. The memory array includes a plurality of magnetic memory cellsarranged in rows and columns. Each of the plurality of magnetic memorycells includes a magnetic storage portion having a different resistancevalue according to a level of storage data written when a data writemagnetic field applied by first and second data write currents is largerthan a predetermined magnetic field. The plurality of read word linesare provided corresponding to the respective rows of the magnetic memorycells, and are driven to a first voltage according to a row selectionresult in a data read operation. The plurality of write word lines areprovided corresponding to the respective rows, and are selectivelyactivated according an address selection result so as to pass the firstdata write current therethrough in a data write operation. The pluralityof bit lines are provided corresponding to the respective columns of themagnetic memory cells so as to extend in such a direction that crossesthe plurality of write word lines, and are each coupled to the magneticstorage portions. One of the plurality of bit lines that is selectedaccording to an address selection result passes therethrough a data readcurrent and the second data write current in the data read operation andthe data write operation, respectively. Each of the magnetic memorycells further includes a rectifying element connected between thecorresponding magnetic storage portion and the corresponding read wordline.

Such a magnetic memory cell using the rectifying element is advantageousin terms of improved integration, and the OFF state of the rectifyingelement can be reliably maintained in the non-selected magnetic memorycells. As a result, the improved integration can be achieved as well asthe operation reliability can be ensured.

According to a yet further aspect of the present invention, a thin filmmagnetic memory device includes a memory array, a plurality of read wordlines, a plurality of write word lines, a plurality of write data lines,and a plurality of read data lines. The memory array includes aplurality of magnetic memory cells arranged in rows and columns. Each ofthe plurality of magnetic memory cells includes a magnetic storageportion having a different resistance value according to a level ofstorage data written when a data write magnetic field applied by firstand second data write currents is larger than a predetermined magneticfield, and a memory cell selection gate for passing a data read currenttherethrough into the magnetic storage portion in a data read operation.The plurality of read word lines are provided corresponding to therespective rows of the magnetic memory cells, for actuating thecorresponding memory cell selection gate according to an addressselection result in the data read operation. The plurality of write wordlines are provided corresponding to the respective columns of themagnetic memory cells, and are selectively driven to an active stateaccording to an address selection result so as to pass the first datawrite current therethrough in a data write operation. The plurality ofwrite data lines are provided corresponding to the respective rows, forpassing the second data write current therethrough in the data writeoperation. The plurality of read data lines are provided correspondingto the respective columns, for passing the data read currenttherethrough in the data read operation. Adjacent magnetic memory cellsshare a corresponding one of at least one of the plurality of write wordlines, the plurality of read word lines and the plurality of data lines.

Thus, the read word lines and the write word lines are providedcorresponding to the rows and columns of the magnetic memory cells,respectively, and respective circuits for selectively driving the readword lines and the write word lines are provided independently.Accordingly, the freedom of layout can be improved. Moreover, at leastone of the write word lines, read word lines, write data lines, and readdata lines are shared between corresponding adjacent memory cells,whereby a wiling pitch in the memory array can be widened. As a result,the integration degree of the MRAM device can be improved.

According to a yet further aspect of the present invention, a thin filmmagnetic memory device includes a memory array, a plurality of read wordlines, a plurality of write data lines, a plurality of common lines, anda current control circuit. The memory array includes a plurality ofmagnetic memory cells arranged in rows and columns. Each of theplurality of magnetic memory cells includes a magnetic storage portionhaving a different resistance value according to a level of storage datawritten when a data write magnetic field applied by first and seconddata write currents is larger than a predetermined magnetic field, and amemory cell selection gate for passing a data read current (Is)therethrough into the magnetic storage portion in a data read operation.The plurality of read word lines are provided corresponding to therespective rows of the magnetic memory cells, for actuating thecorresponding memory cell selection gate according to an addressselection result in the data read operation. The plurality of write datalines are provided corresponding to the respective rows, for passing thefirst data write current therethrough in a data write operation. Theplurality of common lines are provided corresponding to the respectivecolumns of the magnetic memory cells. Each of the plurality of commonlines selectively receives supply of the data read current according tothe address selection result in the data read operation. Each of theplurality of common lines is selectively driven to a first voltage (Vcc)for passing the second data write current therethrough according to theaddress selection result in the data write operation. The currentcontrol circuit electrically couples and disconnects each of the commonlines to and from a second voltage (Vss) in the data write operation andthe data read operation, respectively. The second voltage is differentfrom the first voltage. Adjacent magnetic memory cells share acorresponding one of at least one of the plurality of write data lines,the plurality of read word lines and the plurality of common lines.

Thus, each common line functions as a read data line in the data readoperation, and as a write word line in the data write operation, wherebythe number of wirings can be reduced. A circuit for selectively drivingthe read word lines and a circuit for selectively driving the commonlines in the data write operation, i.e., the common lines functioning aswrite word lines, are provided independently, whereby the freedom oflayout can be improved. Moreover, at least one of the read word lines,write data lines and common lines are shared between correspondingadjacent memory cells, whereby a wiling pitch in the memory array can bewidened. As a result, the integration degree of the MRAM device can beimproved.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing the overall structure of anMRAM device 1 according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the first embodiment.

FIG. 3 is a circuit diagram showing the structure of a data writecircuit 51 a of FIG. 2.

FIG. 4 is a circuit diagram showing the structure of a data read circuit55 a of FIG. 2.

FIG. 5 is a timing chart illustrating the data read and write operationsin the MRAM device according to the first embodiment.

FIG. 6 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of the firstembodiment.

FIG. 7 is a circuit diagram showing the structure of a data writecircuit 51 b of FIG. 6.

FIG. 8 is a circuit diagram showing the structure of a data read circuit55 b of FIG. 6.

FIG. 9 is a timing chart illustrating the data read and write operationsin an MRAM device according to the first modification of the firstembodiment.

FIG. 10 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of the firstembodiment.

FIG. 11 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of the firstembodiment.

FIG. 12 is a circuit diagram showing the structure of a data writecircuit according to a second embodiment of the present invention.

FIG. 13 is a circuit diagram-showing an example of the structure of aword line driver according to the second embodiment.

FIG. 14 is a circuit diagram showing the structure of a data writecurrent adjustment circuit 230 according to a modification of the secondembodiment.

FIG. 15 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry in an MRAM device for conducting a data readoperation without using any read gate.

FIG. 16 is a block diagram illustrating the bit line arrangementaccording to a third embodiment of the present invention.

FIG. 17 is a structural diagram showing a first example of the bit linearrangement according to the third embodiment.

FIG. 18 is a structural diagram showing a second example of the bit linearrangement according to the third modification.

FIG. 19 is a conceptual diagram illustrating the bit line arrangementaccording to a first modification of the third embodiment.

FIG. 20 is a structural diagram illustrating the arrangement of a writeword line WWL according to a second modification of the thirdembodiment.

FIGS. 21A and 21B are conceptual diagrams illustrating the couplingbetween sub-word lines forming the same write word line.

FIG. 22 is a diagram illustrating the write word line arrangementaccording to a third modification of the third embodiment.

FIG. 23 is a diagram illustrating the write word line arrangementaccording to a fourth modification of the third embodiment.

FIG. 24 is a diagram illustrating the write word line arrangementaccording to a fifth modification of the third embodiment.

FIG. 25 is a diagram showing the structure of an MTJ memory cellaccording to a fourth embodiment of the present invention.

FIG. 26 is a structural diagram of the MTJ memory cell of FIG. 25provided on a semiconductor substrate.

FIG. 27 is a timing chart illustrating the read and write operationsfrom and to the MTJ memory cell of FIG. 25.

FIG. 28 is a conceptual diagram showing the structure of a memory arrayhaving the MTJ memory cells of FIG. 25 arranged in rows and columns.

FIG. 29 is a conceptual diagram showing the structure of a memory arrayin which the MTJ memory cells arranged in rows and columns share writeword lines WWL.

FIG. 30 is a conceptual diagram showing the MTJ memory cell arrangementaccording to a modification of the fourth embodiment.

FIG. 31 is a schematic block diagram showing the overall structure of anMRAM device 2 according to a fifth embodiment of the present invention.

FIG. 32 is a circuit diagram showing the connection of an MTJ memorycell according to the fifth embodiment.

FIG. 33 is a timing chart illustrating the data read and writeoperations from and to the MTJ memory cell according to the fifthembodiment.

FIG. 34 is a structural diagram illustrating the MTJ memory cellarrangement according to the fifth embodiment.

FIG. 35 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the fifth embodiment.

FIG. 36 is a circuit diagram showing the structure of a data readcircuit 55 e.

FIG. 37 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of the fifthembodiment.

FIG. 38 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of the fifthembodiment.

FIG. 39 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of the fifthembodiment.

FIG. 40 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fourth modification of the fifthembodiment.

FIG. 41 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fifth modification of the fifthembodiment.

FIG. 42 is a circuit diagram showing the connection of an MTJ memorycell according to a sixth embodiment of the present invention.

FIG. 43 is a structural diagram illustrating the MTJ memory cellarrangement according to the sixth embodiment.

FIG. 44 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the sixth embodiment.

FIG. 45 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of the sixthembodiment.

FIG. 46 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of the sixthembodiment.

FIG. 47 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of the sixthembodiment.

FIG. 48 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fourth modification of the sixthembodiment.

FIG. 49 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fifth modification of the sixthembodiment.

FIG. 50 is a circuit diagram showing the connection of an MTJ memorycell according to a seventh embodiment of the present invention.

FIG. 51 is a structural diagram showing the MTJ memory cell arrangementaccording to the seventh embodiment.

FIG. 52 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the seventh embodiment.

FIG. 53 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of theseventh embodiment.

FIG. 54 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of theseventh embodiment.

FIG. 55 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of theseventh embodiment.

FIG. 56 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fourth modification of theseventh embodiment.

FIG. 57 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fifth modification of theseventh embodiment.

FIG. 58 is a circuit diagram showing the connection of an MTJ memorycell according to an eighth embodiment of the present invention.

FIG. 59 is a structural diagram showing the MTJ memory cell arrangementaccording to the eighth embodiment.

FIG. 60 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the eighth embodiment.

FIG. 61 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of the eighthembodiment.

FIG. 62 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of theeighth embodiment.

FIG. 63 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of the eighthembodiment.

FIG. 64 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fourth modification of theeighth embodiment.

FIG. 65 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fifth modification of the eighthembodiment.

FIG. 66 is a circuit diagram showing the connection of an MTJ memorycell according to a ninth embodiment of the present invention.

FIG. 67 is a timing chart illustrating the data write and read operationto and from the MTJ memory cell according to the ninth embodiment.

FIG. 68 is a structural diagram showing the MTJ memory cell arrangementaccording to the ninth embodiment.

FIG. 69 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the ninth embodiment.

FIG. 70 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of the ninthembodiment.

FIG. 71 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of the ninthembodiment.

FIG. 72 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of the ninthembodiment.

FIG. 73 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fourth modification of the ninthembodiment.

FIG. 74 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fifth modification of the ninthembodiment.

FIG. 75 is a circuit diagram showing the connection of an MTJ memorycell according to a tenth embodiment of the present invention.

FIG. 76 is a structural diagram showing the MTJ memory cell arrangementaccording to the tenth embodiment.

FIG. 77 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to the tenth embodiment.

FIG. 78 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a first modification of the tenthembodiment.

FIG. 79 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a second modification of the tenthembodiment.

FIG. 80 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a third modification of the tenthembodiment.

FIG. 81 is a diagram illustrating the structure of memory array 10 andits peripheral circuitry according to a fourth modification of the tenthembodiment.

FIG. 82 is a diagram illustrating the structure of a memory array 10 andits peripheral circuitry according to a fifth modification of the tenthembodiment.

FIG. 83 is a schematic diagram showing the structure of a memory cellhaving a magnetic tunnel junction.

FIG. 84 is a conceptual diagram illustrating the data read operationfrom the MTJ memory cell.

FIG. 85 is a conceptual diagram illustrating the data write operation tothe MTJ memory cell.

FIG. 86 is a conceptual diagram illustrating the relation between thedirection of a data write current and the direction of a magnetic fieldin the data write operation.

FIG. 87 is a conceptual diagram showing the MTJ memory cells arranged inrows and columns in an integrated manner.

FIG. 88 is a structural diagram of the MTJ memory cell provided on asemiconductor substrate.

FIG. 89 is a conceptual diagram illustrating the effects of themanufacturing variation on the data write margin.

FIG. 90 is a schematic diagram showing the structure of an MTJ memorycell using a diode.

FIG. 91 is a structural diagram of the MTJ memory cell of FIG. 90provided on a semiconductor substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

First Embodiment

Referring to FIG. 1, an MRAM device 1 according to the first embodimentof the present invention conducts random access in response to anexternal control signal CMD and address signal ADD, thereby conductinginput of write data DIN and output of read data DOUT.

The MRAM device 1 includes a control circuit 5 for controlling theoverall operation of the MRAM device 1 in response to the control signalCMD, and a memory array 10 having a plurality of MTJ memory cellsarranged in n rows by m columns. Although the structure of the memoryarray 10 will be described later in detail, a plurality of write wordlines WWL and a plurality of read word lines RWL are providedcorresponding to the respective MTJ memory cell rows. Folded bit linepairs are provided corresponding to the respective MTJ memory cellcolumns. Each bit line pair is formed from bit lines BL and /BL. Notethat, hereinafter, a set of bit lines BL and /BL is also generallyreferred to as a bit line pair BLP.

The MRAM device 1 further includes a row decoder 20 for conducting rowselection in the memory array 10 according to a row address RA indicatedby the address signal ADD, a column decoder 25 for conducting columnselection in the memory array 10 according to a column address CAindicated by the address signal ADD, a word line driver 30 forselectively activating the read word line RWL and write word line WWLbased on the row selection result of the row decoder 20, a word linecurrent control circuit 40 for applying a data write current to thewrite word line WWL in the data write operation, and read write controlcircuits 50, 60 for applying a data write current ±Iw and a sensecurrent Is in the data read and write operations.

Referring to FIG. 2, the memory array 10 includes the MTJ memory cellsMC arranged in n rows by m columns (n, m: a natural number). The MTJmemory cells MC have the structure shown in FIG. 83. The read word linesRWL1 to RWLn and the write word lines WWL1 to WWLn are providedcorresponding to the respective MTJ memory cell rows (hereinafter, alsosimply referred to as “memory cell rows”). The bit lines BL1, /BL1 toBLm, /BLm forming the bit line pairs BLP1 to BLPm are providedcorresponding to the respective MTJ memory cell columns (hereinafter,also simply referred to as “memory cell columns”).

The MTJ memory cells MC in each row are coupled to either the bit linesBL or the bit lines /BL in an alternate manner. For example, for the MTJmemory cells in the first memory cell column, the MTJ memory cell in thefirst row is coupled to he bit line /BL1, whereas the MTJ memory cell inthe second row is coupled to the bit line BL1. Similarly, the MTJ memorycells in the odd rows are each connected to one bit line (/BL1 to /BLm)of a corresponding bit line pair, and the MTJ memory cells in the evenrows are each connected to the other bit line (BL1 to BLm) of acorresponding bit line pail.

The memory array 10 further includes a plurality of dummy memory cellsDMC respectively coupled to the bit lines BL1, /BL1 to BLm to /BLm. Thedummy memory cells DMC are each coupled to either a dummy read word lineDRWL1 or DRWL2, and are arranged in two rows by m columns. The dummymemory cells coupled to the dummy read word line DRWL1 are respectivelycoupled to the bit lines BL1, BL2, . . . BLm. The remaining dummy memorycells coupled to the dummy read word line DRWL2 are respectively coupledto the bit lines /BL1, /BL2 . . . /BLm.

As described before, the resistance value of the MTJ memory cell MCvaries according to the storage data level. Assuming that the MTJ memorycell MC storing H-level data has a resistance value Rh and the memorycell MC storing L-level data has a resistance value Rl, a resistancevalue Rd of the dummy memory cell DMC is set to an intermediate value ofRl and Rh. Note that Rl<Rh in the embodiment of the present invention.

Hereinafter, the write word lines, read word lines, dummy read wordlines, bit lines and bit line pairs are also generally denoted with WWL,RWL, DRWL, BL (/BL) and BLP, respectively. A specific write word line,read word line, bit line, and bit line pair are denoted with, forexample, WWL1, RWL1, BL1 (/BL1) and BLP1, respectively.

The write word lines WWL1 to WWLn are coupled to the ground voltage Vssby the word line current control circuit 40. Thus, a data write currentIp is applied to a write word line WWL activated to the selected state(high voltage state: power supply voltage Vcc) by the word line driver30.

Hereinafter, the high voltage state (power supply voltage Vcc) and lowvoltage state (ground voltage Vss) of a signal line are also simplyreferred to as H level and L level, respectively.

Write column selection lines WCSL1 to WCSLm for conducting columnselection in the data write operation are provided corresponding to therespective memory cell columns. Similarly, read column selection linesRCSL1 to RCSLm for conducting column selection in the data readoperation are provided corresponding to the respective memory cellcolumns.

In the data write operation, the column decoder 25 activates one of thewrite column selection lines WCSL1 to WCSLm to the selected state (Hlevel) according to the decode result of the column address CA, i.e.,the column selection result. In the data read operation, the columndecoder 25 activates one of the read column selection lines RCSL1 toRCSLm to the selected state (H level) according to the column selectionresult.

Moreover, a write data bus pair WDBP for transmitting the write data anda read data bus pair RDBP for transmitting the read data are providedindependently. The write data bus pair WDBP includes write data busesWDB and /WDB. Similarly, the read data bus pair RDBP includes read databuses RDB and /RDB.

The read/write control circuit 50 includes a data write circuit 51 a, adata read circuit 55 a, write column selection gates WCSG1 to WCSGm,read column selection gates RCSG1 to RCSGm and read gates RG1 to RGm.The write column selection gates WCSG1 to WCSGm, read column selectiongates RCSG1 to RCSGm and read gates RG1 to RGm are providedcorresponding to the respective memory cell columns.

One of the write column selection gates WCSG1 to WCSGm is turned ONaccording to the column selection result of the column decoder 25 so asto couple the write data buses WDB and /WDB of the write data bus pairWDBP to the corresponding bit lines BL and /BL, respectively.

For example, the write column selection gate WCSG1 includes an N-typeMOS transistor coupled between the write data bus WDB and the bit lineBL1, and an N-type MOS transistor electrically coupled between the writedata bus /WDB and the bit line /BL1. These MOS transistors are turnedON/OFF according to the voltage level on the write column selection lineWCSL1. More specifically, when the write column selection line WCSL1 isactivated to the selected state (H level), the write column selectiongate WCSG1 electrically couples the write data buses WDB and /WDB to thebit lines BL1 and /BL1, respectively. The write column selection gatesWCSG2 to WCSGm provided respectively corresponding to the other memorycell columns also have the same structure as that described above.

The data write circuit 51 a operates in response to a control signal WEthat is activated (to H level) in the data write operation and a controlsignal RE activated (to H level) in the data read operation.

Note that, hereinafter, the read column selection lines RCSL1 to RCSLm,write column selection lines WCSL1 to WCSLm, read column selection gatesRCSG1 to RCSGm, write column selection gates WCSG1 to WCSGm, and readgates RG1 to RGm are also generally denoted with RCSL, WCSL, RCSG, WCSGand RG, respectively.

Referring to FIG. 3, the data write circuit 51 a includes a data writecurrent supply circuit 52 for supplying the data write current ±Iw, anda pull-up circuit 53 for pulling up the bit line BL, /BL in the dataread operation.

The data write current supply circuit 52 includes a P-type MOStransistor 151 for supplying a constant current to an internal node Nw0,and a P-type MOS transistor 152 and current source 153 which form acurrent-mirror circuit for controlling a passing current through thetransistor 151.

The data write current supply circuit 52 further includes inverters 154,155 and 156 operating in response to an operating current supplied fromthe internal node Nw0. The inverter 154 inverts the voltage level of thewrite data DIN for transmission to an internal node Nw1. The inverter155 inverts the voltage level of the write data DIN for transmission tothe input node of the inverter 156. The inverter 156 inverts the outputof the inverter 155 for transmission to-an internal node Nw2. Thus, thedata write circuit 51a sets the voltage on the internal node Nw1 to oneof the power supply voltage Vcc and ground voltage Vss and the voltageon the internal node Nw2 to the other, according to the voltage level ofthe write data DIN.

The pull-up circuit 53 includes P-type MOS transistors 157 and 158electrically coupled between the power supply voltage Vcc and nudes Np1and Np2, respectively. The transistors 157 and 158 receive an invertedsignal /RE of the control signal RE at their gates.

The data write circuit 51a further includes a switch SW1 a forselectively coupling one of the nodes Nw1 and Np1 to the write data busWDB, and a switch SWb for selectively coupling one of the nodes Nw2 andNp2 to the write data bus /WDB. The switches SW1 a and SW1 b operate inresponse to a control signal RWS.

In the data write operation, the switches SW1 a and SW1 b connect thenodes Nw1 and Nw2 to the write data buses WDB and /WDB, respectively. Asa result, in the data write operation, the voltage on the write data busWDB is set to one of the power supply voltage Vcc and ground voltage Vssas well as the voltage on the write data bus /WDB to the other,according to the write data level, in order to supply the data writecurrent ±Iw.

On the other hand, in the data read operation, the switches SW1 a andSW1 b couple the nodes Np1 and Np2 to the write data buses WDB and /WDB,respectively. As a result, in the data read operation, the write databuses WDB and /WDB are pulled up to the power supply voltage Vcc by thepull-up circuit 53.

Referring back to FIG. 2, since each of the read column selection gateRCSG1 to RCSGm and each of the read gates RG1 to RGm, both providedcorresponding to the respective memory cell columns, have the samestructure, the respective structures of the read column selection gateRCSG1 and the read gate RG1 provided corresponding to the bit lines BL1,/BL1 are herein described exemplarily.

The read column selection gate RCSG1 and the read gate RG1 are coupledin series between the read data bus RDB, /RDB and the ground voltageVss.

The read column selection gate RCSG1 includes an N-type MOS transistorcoupled between the read data bus RDB and a node N1 a, and an N-type MOStransistor electrically coupled between the read data bus /RDB and anode N1 b. These MOS transistors are turned ON/OFF according to thevoltage on the read column selection line RCSL1. More specifically, whenthe read column selection line RCSL1 is activated to the selected state(H level), the read column selection gate RCSG1 electrically couples theread data buses RDB and /RDB to the nodes N1 a and N1 b, respectively.

The read gate RG1 includes N-type MOS transistors Q11 and Q12electrically coupled between the ground voltage Vss and the nodes N1 aand N1 b, respectively. The transistors Q1 and Q2 have their gatescoupled to the bit lines /BL1 and BL1, respectively. Accordingly, thevoltages on the nodes N1 a and N1 b change according to the voltages onthe bit lines /BL1 and BL1, respectively.

More specifically, when the voltage on the bit line BL1 is higher thanthat on the bit line /BL1, the node N1 b are strongly pulled down towardthe ground voltage Vss by the transistor Q12. Therefore, the voltage onthe node N1 a becomes higher than that on the node N1 b. On thecontrary, when the voltage on the bit line BL1 is lower than that on thebit line /BL1, the voltage on the node N1 b becomes higher than that onthe node N1 a.

The voltage difference between the nodes N1 a and N1 b thus produced istransmitted into the voltage difference between the read data buses RDBand /RDB through the read column selection gate RCSG1. The data readcircuit 55 a amplifies the voltage difference between the read databuses RDB and /RDB of the read data bus pair RDBP so as to produce theread data DOUT.

Referring to FIG. 4, the data read circuit 55 a includes a differentialamplifier 56. In response to the voltages on the read data buses RDB and/RDB, the differential amplifier 56 amplifies the voltage differencetherebetween so as to produce the read data DOUT.

Referring back to FIG. 2, the read/write control circuit 60 includesequalizing transistors 62-1 to 62-m that are turned ON/OFF according toa bit line equalizing signal BLEQ. The equalizing transistors 62-1 to62-m are provided corresponding to the respective memory cell columns.For example, the equalizing transistor 62-1 corresponds to the firstmemory cell, and electrically couples the bit lines BL1 and /BL1 to eachother in response to activation (H level) of the bit line equalizingsignal BLEQ.

Similarly, the equalizing transistors 62-2 to 62-m respectivelycorresponding to the other memory cell columns electrically couple thebit lines BL and /BL of the bit line pair BLP to each other in thecorresponding memory cell column, in response to activation of the bitline equalizing signal BLEQ.

The read/write control circuit 60 further includes prechargingtransistors 64-1 a, 64-1 b to 64-ma, 64-mb respectively provided betweenthe ground voltage Vss and the bit lines BL1, /BL1 to bit lines BLm,/BLm. The precharging transistors 64-1 a, 64-1 b to 64-ma, 64-mb areturned ON in response to activation of a bit line precharging signalBLPR so as to precharge the bit lines BL1, /BL1 to bit lines BLm, /BLmto the ground voltage Vss, respectively.

Note that, hereinafter, the equalizing transistors 62-1 to 62-m andprecharging transistors 64-1 a, 64-1 b to 64-ma, 64-mb are alsogenerally referred to as equalizing transistors 62 and prechargingtransistors 64, respectively.

In the stand-by period of the MRAM device 1 as well as in the periodother than the data read operation in the active period of the MRAMdevice 1, the bit line equalizing signal BLEQ produced by the controlcircuit 5 is activated to H level in order to short-circuit the bitlines BL and /BL of each folded bit line pair BL.

On the other hand, in the data read operation in the active period ofthe MRAM device 1, the bit line equalizing signal BLEQ is inactivated toL level. In response to this, the bit lines BL and /BL of each bit linepair BL in each memory cell column are electrically disconnected fromeach other.

The bit line precharging signal BLPR is also produced by the controlcircuit 5. In the active period of the MRAM device 1, the bit lineprecharging signal BLPR is activated to H level at least during aprescribed period before the data read operation. During the data readoperation in the active period of the MRAM device 1, the bit lineprecharging signal BLPR is inactivated to L level, so that theprecharging transistors 64 are turned OFF.

Hereinafter, the data read and write operations of the MRAM deviceaccording to the first embodiment will be described with reference toFIG. 5.

First, the data write operation will be described.

Referring to FIG. 5, the write column selection line WCSL correspondingto the column selection result is activated to the selected state (Hlevel), so that the corresponding write column selection gate WCSG isturned ON. In response to this, the bit lines BL and /BL correspondingto the column selection result are respectively coupled to the writedata buses WDB and /WDB.

Moreover, in the data write operation, the equalizing transistor 62 isturned ON to short-circuit the bit lines BL and /BL.

As described before, the data write circuit 51 a sets the voltage on thewrite data bus WDB to one of the power supply voltage Vcc and groundvoltage Vss, and the voltage on the write data bus /WDB to the other.For example, in the case where the write data DIN is L-level data, thevoltages on the nodes Nw2 and Nw1 shown in FIG. 3 are respectively setto the power supply voltage Vcc and the ground voltage Vcc. Therefore,the data write current −Iw for writing the L level data is applied tothe write data bus WDB. The data write current ±Iw is supplied to thebit line BL through the write column selection gate WCSG.

The data write current −Iw flowing through the bit line BL turns aroundat the equalizing transistor 62. Thus, the data write current +Iw of theopposite direction flows through the other bit line /BL. The data writecurrent +Iw flowing through the bit line /BL is transmitted to the writedata bus /WDB through the write column selection gate WCSG.

Moreover, one of the write word lines WWL is activated to the selectedstate (H level) according to the row selection result, and the datawrite current Ip is applied thereto. Accordingly, in the memory cellcolumn corresponding to the column selection result, the data is writtento the MTJ memory cell corresponding to the selected write word lineWWL. At this time, the L-level data is written to the memory cell MCcoupled to the bit line BL, whereas the H level data is written to thememory cell MC coupled to the bit line /BL.

In the case where the write data DIN is H-level data, the voltages onthe nodes Nw1 and Nw2 are set in the opposite manner to that describedabove. Therefore, the data write current flows through the bit lines BLand /BL in the opposite direction to that described above for the datawrite operation. Thus, the data write current ±Iw having the directioncorresponding to the level of the write data DIN is supplied to the bitlines BL and /BL.

In the data write operation, the read word lines RWL are retained in thenon-selected state (L level).

For example, by activating the bit line precharging signal BLPR (to Hlevel) in the data write operation, the voltages on the bit lines BL and/BL in the data write operation are set to the ground voltage Vsscorresponding to the precharge voltage level for the data readoperation.

Similarly, the read data buses RDB and /RDB are set to the power supplyvoltage Vcc corresponding to the precharge voltage for the data readoperation. Thus, the voltages on the bit lines BL, /BL and the read databuses RDB, /RDB corresponding to the non-selected columns in the datawrite operation correspond to the precharge voltage for the data readoperation. This eliminates the need to conduct an additional prechargingoperation before the data read operation, increasing the speed of thedata read operation.

Hereinafter, the data read operation will be described.

Before the data read operation, the read data buses RDB, /RDB and thebit lines BL, /BL are precharged to the power supply voltage Vcc and theground voltage Vss, respectively.

In the data read operation, the write data buses WDB and /WDB are pulledup to the power supply voltage Vcc by the pull-up circuit 53. Moreover,according to the column selection result, both a corresponding readcolumn selection line RCSL and a corresponding write column selectionline WCSL are activated to the selected state (H level).

Thus, the write data buses WDB and /WDB are electrically coupled to thebit lines BL and /BL of the selected column through the write columnselection gate WCSG, respectively. Accordingly, in the data readoperation, the bit lines BL and /BL corresponding to the selected memorycell column are pulled up to the power supply voltage Vcc.

One of the read word lines RWL is activated to the selected state (Hlevel) according to the row selection result, whereby the correspondingmemory cell MC is coupled to one of the bit lines BL and /PL.

Moreover, one of the dummy read word lines DRWL1 and DRWL2 is activated,whereby the other of the bit lines BL and /BL, which is not coupled tothe MTJ memory cell MC, is coupled to the dummy memory cell DMC.

In the case where an odd row is selected according to the row selectionresult and the bit line /BL is coupled to the MTJ memory cell MC, thedummy read word line DRWL1 is activated, so that the bit line BL iscoupled to the dummy memory cell DMC. On the contrary, in the case wherean even row is selected according to the row selection result and thebit line BL is coupled to the MTJ memory cell MC, the dummy read wordline DRWL2 is activated, so that the bit line /BL is coupled to thedummy memory cell DMC.

In the selected MTJ memory cell MC, the access transistor ATR is turnedON, whereby the sense current Is flows through a path of the pulled-upbit line BL or /BL, memory cell MC and ground voltage Vss. Accordingly,a voltage change ΔV1 corresponding to the stored data level is producedon one of the bit lines BL and /BL, which is coupled to the MTJ memorycell. FIG. 5 exemplarily shows a voltage change for the case where theMTJ memory cell MC to be read retains H-level data, that is, the MTJmemory cell MC to be read has a resistance value Rh.

As described above, the resistance value Rd of the dummy memory cell DMCis set to an intermediate value of the resistance values Rh and Rl ofthe MTJ memory cell MC. Accordingly, a voltage change ΔVm correspondingto the intermediate resistance value Rd is produced on the other of thebit lines BL and /BL, which is coupled to the dummy memory cell DMC.

Accordingly, the relative relation between the voltages on the bit linesBL and /BL of the bit line pair BLP corresponding to the selected memorycell column changes according to the read storage data level. With sucha voltage difference between the bit lines BL and /BL, the read databuses RDB and /RDB are driven through the read gate.

More specifically, when the voltage on the bit line BL is higher thanthat on the bit line /BL, the read data bus /RDB is more strongly driventoward the ground voltage Vss through the read gate RG than is the readdata bus RDB (the voltage change ΔVb1>ΔVbm in FIG. 5). The voltagedifference between the read data buses RDB and /RDB thus produced isamplified by the data read circuit 55 a, so that the H-level read dataDOUT can be output.

On the contrary, in the case where the MTJ memory cell MC to be readretains L-level data, that is, in the case where the voltage on the bitline /BL is higher than that on the bit line BL, the read data bus RDBis more strongly driven toward the ground voltage Vss through the readgate RG than is the read data bus /RDB. The voltage difference betweenthe read data buses RDB and /RDB thus produced is amplified by the dataread circuit 52, so that the L-level read data DOUT can be output.

Thus, driving the read data buses RDB and /RDB through the read gate RGenables the data read operation to be conducted without applying thesense current to the read data buses RDB and /RDB. This reduces the RCload on the sense current path, whereby a voltage change required toread the data can be quickly produced on the bit lines BL and /BL. Thus,the data can be read at a high speed, whereby the access speed to theMRAM device can be increased.

Moreover, the pulled-up write data buses WDB and /WDB are respectivelycoupled to the bit lines BL and /BL through the write column selectiongate WDSG so as to supply the sense current Is. Therefore, the sensecurrent Is can be applied only to the bit lines BL and /BL correspondingto the memory cell column to be read. This can avoid unnecessary currentconsumption in the data read operation.

Moreover, the folded bit line pair causes the data write current to turnaround at the equalizing transistor. Therefore, the data write currentof the different directions can be supplied merely by controlling oneend of the bit line BL to one of the power supply voltage Vcc and groundvoltage Vss and one end of the bit line /BL to the other. Thus, avoltage of different polarity (negative voltage) is not necessary, andthe direction of the current can be switched merely by setting thevoltage on the write data bus WDB to one of the power supply voltage andground voltage and the voltage on the write data bus /WDB to the other.Accordingly, the structure of the data write circuit 51 a can besimplified. Moreover, the structure for sinking the data write current±Iw (i.e., a current path to the ground voltage Vss) need not beprovided in the read/write control circuit 60, and the data writecurrent +Iw can be controlled only with the equalizing transistor 62. Asa result, the circuit structure associated with the data write current±Iw within the read/write control circuits 50 and 60 can be reduced insize.

Moreover, since the data read operation is conducted using the dummymemory cells in the structure having the folded bit line pairs, asufficient data read margin can be ensured.

First Modification of First Embodiment

Referring to FIG. 6, the structure according to the first modificationof the first embodiment is different from that of the first embodimentin that the precharging transistors 64-1 a, 64-1 b to 64-m 1 to 64-mbare provided in order to precharge the bit lines BL1, /BL1 to BLm, /BLmto the power supply voltage Vcc. Moreover, the data write circuit 51 aand the data read circuit 55 a are replaced with a data write circuit 51b and data read circuit 55 b, respectively. Since the structure isotherwise the same as that of the first embodiment shown in FIG. 2,detailed description thereof will not be repeated.

Referring to FIG. 7, the data write circuit 51 b includes the data writecurrent supply circuit 52 shown in FIG. 3. The data write circuit 51 bcouples the output nodes Nw1 and Nw2 of the data write current supplycircuit 52 directly to the write data bus pair WDB and /WDB,respectively. The data write circuit 51 b does not include the pull-upcircuit 53 and the switches SW1 a, SW1 b, and does not conduct thepull-up operation in the data read operation.

Referring to FIG. 8, the data read circuit 55 b includes transfer gatesTGa and TGb respectively provided between the read data buses RDB, /RDBand the input nodes of the differential amplifier 56. The transfer gatesTGa and TGb couple the read data buses RDB and /RDB to the respectiveinput nodes of the differential amplifier 56 according to a triggerpulse φr.

The data read circuit 55b further includes a latch circuit 57 forlatching the output of the differential amplifier 56, and a transfergate TGc provided between the differential amplifier 56 and the latchcircuit 57. Like the transfer gates TGa and TGb, the transfer gate TGcoperates in response to the trigger pulse φr. The latch circuit 57outputs the read data DOUT.

Accordingly, at the timing the trigger pulse φr is activated to H level,the data read circuit 55 b amplifies the voltage difference between theread data buses RDB and /RDB so as to set the level of the read dataDOUT. During the inactive (L level) period of the trigger pulse φr, thelevel of the read data DOUT is retained in the latch circuit 57.

Hereinafter, the data read and write operations of the MRAM deviceaccording to the first modification of the first embodiment will bedescribed with reference to FIG. 9.

Referring to FIG. 9, the precharge voltage of the bit lines BL and /BLbefore the data write operation is set to the power supply voltage Vcc.In the data write operation, the trigger pulse φr is retained in theinactive state (L level). Since the data write operation is otherwisethe same as that shown by the timing chart of FIG. 5, detaileddescription thereof will not be repeated.

Hereinafter, the data read operation will be described. Before the dataread operation, the bit lines BL, /BL and the read data buses RDB, /RDBare precharged to the power supply voltage Vcc. On the other hand, thewrite column selection lines WCSL are retained in the inactive state (Llevel) in the data read operation. In other words, unlike the firstembodiment, the bit lines BL and /BL are not pulled up to the powersupply voltage Vcc in the data read operation.

With the bit lines BL and /BL precharged to the power supply voltageVcc, the read word line RWL is selectively activated according to therow selection result. In response to this, the access transistor ATR isturned ON in the MTJ memory cell to be read, whereby the path of thesense current Is is formed. Thus, the voltage on the bit line BL, /BLstarts reducing.

The voltage reducing rate of the bit line BL, /BL is determined based onthe resistance value of the memory cell MC or dummy memory cell DMCcoupled to the bit line BL, /BL. More specifically, the bit line BL, /BLcoupled to the memory cell MC storing L-level data has a high voltagereducing rate, whereas the bit line BL, /BL coupled to the memory cellMC storing H-level data has a low voltage reducing rate. The bit lineBL, /BL coupled to the dummy memory cell DMC has an intermediate voltagereducing rate.

FIG. 9 exemplarily shows the waveform of the bit line for the case wherethe MTJ memory cell MC to be read retains L-level data. FIG. 9 alsoshows the waveform of the bit line coupled to the dummy memory cell DMC.

As in the first embodiment, the voltage reduction on the bit line BL,/BL is transmitted to the read data bus RDB, /RDB through the read gateRG. Accordingly, the trigger pulse φr is activated at a prescribedtiming during reduction in voltage on the read data bus RDB, /RDB,whereby the voltage difference between the read data buses RDB and /RDBis taken in the latch circuit 57. Thus, the data read operation can beconducted at a high speed as in the first embodiment.

Note that the structure according to the first modification of the firstembodiment eliminates the need to supply the sense current Is in thedata read operation, allowing for further reduction in powerconsumption.

Second Modification of First Embodiment

In the second modification of the first embodiment, the data readoperation through the read gate RG as described in the first embodimentand the first modification thereof is applied to the open bit linestructure.

Referring to FIG. 10, in the structure according to the secondmodification of the first embodiment, open bit lines BL1 to BLm areprovided corresponding to the respective memory cell columns. The writecolumn selection gates WCSG1 to WCSGm are provided between the writedata bus WDB and the bit lines BL1 to BLm, respectively. The writecolumn selection gates WCSG1 to WCSGm are turned ON/OFF according to thevoltage on the respective write column selection lines WCSL1 to WCSLm.

The read/write control circuit 60 includes bit line current controltransistors 63-1 to 63-m provided between the write data bus /WDB andthe bit lines BL1 to BLm, respectively. Like the write column selectiongates WCSG1 to WCSGm, the bit line current control transistors 63-1 to63-m are turned ON/OFF according to the voltage on the respective writecolumn selection lines WCSL1 to WCSLm.

The precharging transistors 64-1 to 64-m precharge the respective bitlines BL1 to BLm to the power supply voltage Vcc in response to the bitline precharging signal BLPR.

As in the case of FIG. 6, the data write circuit 51 b supplies the datawrite current ±Iw to the write data buses WDB and /WDB. With such astructure, the data write current can be supplied to the selected memorycell column as in the case of the first modification of the firstembodiment.

In each memory cell column, the read column selection gate RCSG and theread gate RG are coupled in series between the read data bus RDB and theground voltage Vss. For example, in the first memory cell column, theread column selection gate RCSG1 and the read gate RG1 are coupled inseries between the read data bus RDB and the ground voltage Vss. Theread column selection gate RCSG1 is formed from an N-type MOS transistorthat is turned ON/OFF according to the read column selection line RCSL1,and the read gate RG1 is formed from an N-type MOS transistor having itsgate coupled to the bit line BL1.

With such a structure, the read data bus RDB can be driven according tothe voltage on the corresponding bit line BL through the read gate RG inthe selected memory cell column. Accordingly, when the read word lineRWL is activated with the bit lines BL1 to BLm precharged to the powersupply voltage Vcc, a sense current path of the bit line BL (prechargedto the power supply voltage Vcc), MTJ memory cell and ground voltage Vsscan be formed in the selected memory cell.

Thus, the voltage on the corresponding bit line BL reduces at a ratecorresponding to the storage data level in the selected MTJ memory cellMC. Accordingly, as in the first modification of the first embodiment,the voltage level on the bit line is taken in the data read circuit 55 cat an appropriate timing during reduction in voltage on the read databus RDB, and this -voltage is compared with a reference voltage Vmdetermined based on the voltage reduction rate of the dummy memory cellDMC in the first modification of the first embodiment. As a result, theread data DOUT can be output. In other words, the structure of the dataread circuit 55c can be implemented with the data read circuit 55 c ofFIG. 8 arranged such that one of the input nodes of the differentialamplifier 56 receives the reference voltage Vm instead of the voltage onthe read data bus /RDB.

Note that it is also possible to conduct the same data read operation asthat in the first embodiment with the bit lines BL pulled up to thepower supply voltage Vcc. In such a case, turning ON/OFF of the writecolumn selection gate WCSG and bit line current control transistor 62 iscontrolled in the same manner as that in the first embodiment, and thedata write circuit 51 b is replaced with the data write circuit 51 aincluding the pull-up circuit 53.

In this case, the write column selection gate WCSG is turned ON both inthe data read and write operations according to the column selectionresult, but the bit line current control transistor 62 can be turned ONonly in the data write operation.

Moreover, although the specific structure is not shown in the figure,the data read circuit 55c can be replaced with a differential amplifierfor producing the read data DOUT according to the comparison resultbetween the voltage on the write data bus WDB and the reference voltagethat is set corresponding to the resistance value Rd of the dummy memorycell DMC.

Thus, the same data read and write operations as those of the firstembodiment and the first modification thereof can be conducted even inthe open bit line structure.

Third Modification of First Embodiment

In the third modification of the first embodiment, the number of gatecircuits associated with column selection is reduced.

Referring to FIG. 11, the structure according to the third modificationof the first embodiment includes a data input/output (I/O) line pairDI/OP formed from data I/O lines IO and /IO.

Column selection gates CSG1 to CSGm are provided between the data I/Oline pair DI/OP and the bit line pairs BL-P1 to BLPm, respectively.According to the column selection result, the column selection gate CSG1to CSGm is turned ON/OFF according to the voltage on a correspondingcolumn selection line CSL1 to CSLm that is selectively activated to Hlevel by the column decoder 25. More specifically, both in the data readand write operations, the column selection gate CSG1 to CSGm is turnedON/OFF according to the column selection result.

Note that the column selection gates CSG1 to CSGm are also generallydenoted with CSG.

A read gate for increasing the data read speed is provided as a commonread gate RCG coupled between the read data bus pair RDBP and the dataI/O line pair DI/OP. A write selection gate WCG is further providedbetween the data I/O line pair DI/OP and the write data bus pair WDBP.

Since the respective structures of the memory array 10 and theread/write control circuit 60 are the same as those of FIG. 2, detaileddescription thereof will not be repeated. Moreover, the respectivestructures and operations of the data write circuit 51 a and the dataread circuit 55 a are also the same as those described above. Therefore,detailed description thereof will not be repeated.

The read gate RCG includes N-type MOS transistors Qc1 and Qc3 coupled inseries between the read data bus RDB and the ground voltage Vss, andN-type MOS transistors Qc2 and Qc4 coupled in series between the readdata bus /RDB and the ground voltage Vss. The transistors Qc1 and Qc2receive the control signal RE at their gates. The transistors Qc3 andQc4 are connected at their gates to the data I/O lines /IO and IO,respectively.

Thus, in the data read operation in which the control signal RE isactivated to H level, the read data buses RDB, /RDB can be driven by thebit lines BL, /BL corresponding to the selected memory cell columnthrough the column selection gate CSG and the data I/O line pair DI/OP.

Accordingly, the memory cell columns in the memory array 10 sharing thedata I/O line pair DI/OP share the common read gate RCG, achievingreduction in circuit area. With the common read gate RCG as well, thedata read operation can be conducted at a high speed without supplyingthe sense current Is to the read data buses RDB, /RDB.

The write selection gate WCG includes an N-type MOS transistor Qc5electrically coupled between the write data bus WDB and the data I/Oline IO, and an N-type MOS transistor Qc6 electrically coupled betweenthe write data bus /WDB and the data I/O line /IO. The transistors Qc5and Qc6 receive a control signal SG at their gates. The control signalSG is activated in the data write operation according to the controlsignal WE. In the data read operation as well, the control signal SG maybe activated according to the control signal RE. Thus, the transistorsQc5 and QcG are turned ON, and the pull-up circuit 53 within the datawrite circuit 51 a pulls up the bit lines BL and /BL corresponding tothe selected memory cell column, whereby the sense current Is can besupplied.

In the data write operation, the transistors Qc1 and Qc2 in the commonread gate RCG are turned OFF. Therefore, the voltages on the read databuses RDB and /RDB do not relate to the data I/O lines IO and /IO.

On the other hand, in response to activation (H level) of the controlsignal SG, the transistors Qc5 and Qc6 in the write selection gate WCGelectrically couple the write data buses WDB and /WDB to the data I/Olines IO and /IO, respectively. Thus, the data write current ±Iw can besupplied to the bit lines BL and /BL corresponding to the selectedmemory cell column.

As in the case of FIG. 6, the data write circuit 5la and the data readcircuit 55 a may be replaced with the data write circuit 51 b and thedata read circuit 55 b, and the power supply voltage Vcc may be used asthe precharge voltage of the bit lines BL1, /BL1 to BLm, /BLm. Thus, thedata read operation according to the voltage reduction rate on the bitline can be conducted as in the first modification of the firstembodiment.

In this case, the control signal SG must be inactivated to L level inthe data read operation in order to turn OFF the write selection gateWCG. For example, instead of the control signal SG, the control signalWE can be directly input to the gates of the transistors Qc5 and Qc6.

Second Embodiment

In the second embodiment is described the structure for adjusting a datawrite current in order to ensure a data write margin corresponding tovariation in magnetic characteristics of the memory cells due tomanufacturing variation.

Referring to FIG. 12, a data write circuit according to the secondembodiment is different from the data write circuit 51 a shown in FIG. 3in that the data write current of the second embodiment further includesa data write current adjustment circuit 200.

The data write current adjustment circuit 200 outputs a referencevoltage Vrw for controlling the current amount of the current source 153in the data write current supply circuit 52. The data write currentsupply circuit 52 includes an N-channel MOS transistor receiving thereference voltage Vrw at its gate. This N-channel MOS transistorcorresponds to the current source 153. Accordingly, the current amountsupplied to the node Nw0 through the transistor 151 forming a currentmirror with the transistor 152 in the data write current supply circuit52, i.e., the amount of the data write current ±Iw, can be adjustedaccording to the reference voltage Vrw.

The data write current adjustment circuit 200 includes a referencevoltage external input terminal 202 for receiving an external referencevoltage Vre1, a test input terminal 204 for receiving a test mode entrysignal TE for switching generation of the reference voltage Vrw betweenthe test mode and the normal mode, and an internal reference voltagegeneration circuit 206 for generating an internal reference voltageVri1.

The data write current adjustment circuit 200 further includes atransfer gate TGf1 coupled between the reference voltage external inputterminal 202 and a node Nf1, and a transfer gate TGf2 provided betweenthe internal reference voltage generation circuit 206 and the node Nf1.The transfer gates TGf1 and TGf2 are turned ON in a complementary mannerin response to the test mode entry signal TE. The node Nf1 is coupled tothe gate of the N-channel MOS transistor corresponding to the currentsource 153.

With such a structure, in the normal operation in which the test modeentry signal TE is inactivated to L level, the transfer gates TGf2 andTGf1 are turned ON and OFF, respectively. Accordingly, the referencevoltage Vri1 produced by the internal reference voltage generationcircuit 206 is input as the reference voltage Vrw to the gate of thetransistor corresponding to the current source 153.

On the other hand, in the test operation in which the test mode entrysignal TE is activated to H level, the transfer gates TGf1 and TGf2 areturned ON and OFF, respectively. Accordingly, the external referencevoltage Vre1 applied to the reference voltage external input terminal202 is input to the gate of the transistor corresponding to the currentsource 153.

Accordingly, in the test mode, the external reference voltage Vre1 at anarbitrary level is input in response to activation of the test modeentry signal TE, so that the data write margin can be tested. Thus, themanufacturing variation in magnetic characteristics of the MTJ memorycells can be compensated for, whereby the adjustment testing of the datawrite current amount for appropriately ensuring a data write margin canbe conducted. For example, this adjustment testing can be conducted suchthat the data write current ±Iw is gradually reduced from the standardvalue, whereby whether or not a desired data write margin is ensured forevery MTJ memory cell is confirmed.

The level of the voltage Vri1 produced by the internal reference voltagegeneration circuit 206 need only be set to a proper value of thereference voltage Vrw that is found from such adjustment testing.

Thus, variation in magnetic characteristics of the MTJ memory cells dueto the manufacturing variation can be compensated for, allowing the datawrite operation in the normal operation to be conducted based on aproper data write current amount.

Referring to FIG. 13, a word line driver according to the secondembodiment includes write word drivers WWD1 to WWDn providedcorresponding to the write word lines WWL1 to WWLn, respectively. Eachof the write word drivers WWD1 to WWDn is formed from, e.g., aninverter. Note that, hereinafter, the write word drivers WWD1 to WWDnare also generally denoted with WWD.

The row decoder 20 activates one of row decode signals RD1 to RDn, i.e.,the row decode signal corresponding to the selected row, to L levelaccording to the row address RA. The row decode signals RD1 to RDn aretransmitted to the word line driver 30. The write word drivers WWD1 toWWDn of the word line driver 30 receive the row decode signals RD1 toRDn respectively. When a row decode signal is inactivated to L level,the corresponding write word driver WWD activate the corresponding writeword line WWL to the selected state (H level).

In the data write operation, the write word driver WWD1 to WWDn suppliesthe data write current Ip to the write word line WWL corresponding tothe selected row.

The word line driver 30 further includes a data write current supplycircuit 32 for supplying the data write current Ip to the word driversWWD1 to WWDn, and a data write current adjustment circuit 210 foradjusting the amount of the data write current Ip.

The data write current supply circuit 32 includes P-channel MOStransistors 33 a and 33 b electrically coupled between the power supplyvoltage Vcc and nodes Np0 and Np1, and an N-channel MOS transistor 34electrically coupled between the node Np1 and the ground voltage Vss.The data write current Ip to be supplied to each write word driver WWDis transmitted to the node Np0.

The node Np1 is electrically coupled to the gates of the transistors 33a and 33 b. The transistor 34 receives at its gate a reference voltageVrp output from the data write current adjustment circuit 210. Thus, thetransistor 34 operates as a current source for supplying the currentamount according to the reference voltage Vrp. Since the transistors 33a, 33 b and 34 form a current mirror circuit, the current amountsupplied through the data write current supply circuit 32 to the nodeNp0, i.e., the amount of the data write current Ip, can be adjustedaccording to the reference voltage Vrp output from the data writecurrent adjustment circuit 210.

The data write current adjustment circuit 210 has the same structure asthat of the data write current adjustment circuit 200 described inconnection with FIG. 11.

More specifically, the data write current adjustment circuit 210includes a reference voltage external input terminal 212 for receivingan external reference voltage Vre2, a test input terminal 214 forreceiving a test mode entry signal TE, and an internal reference voltagegeneration circuit 216 for generating an internal reference voltageVri2.

The data write current adjustment circuit 210 further includes atransfer gate TGf3 coupled between the reference voltage external inputterminal 212 and a node Nf2, and a transfer gate TGf4 provided betweenthe internal reference voltage generation circuit 216 and the node Nf2.The transfer gates TGf3 and TGf4 are turned ON in a complementary mannerin response to the test mode entry signal TE. The node Nf2 is coupled tothe gate of the transistor 34 operating as a current source.

Accordingly, in each of the normal operation and the test modeoperation, the reference voltage Vri2 produced by the internal referencevoltage generation circuit 216 and the external reference voltage Vre2applied to the reference voltage external input terminal 212 are inputto the gate of the transistor 34 according to the test mode entry signalTE.

As a result, in the test mode, the external reference voltage Vre2 at anarbitrary level is input, so that the data write margin can be tested.Thus, the manufacturing variation in magnetic characteristics of the MTJmemory cells can be compensated for, whereby the adjustment testing ofthe data write current amount for appropriately ensuring a data writemargin can be facilitated. For example, this adjustment testing can beconducted such that the data write current Ip is gradually reduced fromthe standard value, whereby whether or not a desired data write marginis ensured for every MTJ memory cell is confirmed.

The level of the voltage Vri2 produced by the internal reference voltagegeneration circuit 216 need only be set to a proper value of thereference voltage Vrw that is found from such adjustment testing.

Thus, variation in magnetic characteristics of the MTJ memory cells dueto the manufacturing variation can be compensated for, allowing the datawrite operation in the normal operation to be conducted based on aproper data write current amount.

Modification of Second Embodiment

Referring to FIG. 14, a data write current adjustment circuit 230according to the modification of the second embodiment outputs areference voltage Vref for adjusting the amount of the data writecurrent. Note that the data write current adjustment circuit 230 shownin FIG. 13 may be replaced either with the data write current adjustmentcircuit 200 for adjusting the data write current ±Iw to be supplied tothe bit line or with the data write current adjustment circuit 21 foradjusting the data write current Ip to be supplied to the write wordline.

Referring to FIG. 14, the data write current adjustment circuit 230includes a tuning input portion 231 a and a voltage adjustment portion231 b for adjusting the reference voltage Vref according to the settingof the tuning input portion 231 a.

The voltage adjustment portion 231 b includes a P-channel MOS transistor232 electrically coupled between a node Nt1 producing the referencevoltage Vref and the power supply voltage Vcc, and an operationalamplifier 234 for amplifying the voltage difference between the voltageon a node Nt2 and a prescribed voltage Vref0 for output to the gate ofthe transistor 232.

The voltage adjustment portion 231 b further includes a P-channel MOStransistor 240 electrically coupled between the nodes Nt1 and Nt2, andP-channel MOS transistors 241, 242, 243 and 244 coupled in seriesbetween the node Nt2 and the ground voltage Vss. The transistors 240 to244 have their gates coupled to the ground voltage Vss. Thus, thetransistors 240 to 244 serve as resistive elements.

With the gate voltage of the transistor 232 being controlled by theoperational amplifier 234, the level of the reference voltage Vref iscontrolled so that the voltage on the node Nt2 becomes equal to theprescribed voltage Vref0. The prescribed voltage Vref0 is set in view ofthe reference voltage Vref.

Herein, the voltage Vα on the node Nt2 is obtained from the referencevoltage Vref divided by the transistors 240 to 244 serving as resistiveelements. Provided that this voltage division ratio is defined as α(α=Vref/Vα), the reference voltage Vref is given by the followingexpression using the prescribed voltage Vref0 input to the operationalamplifier 234: Vref=α·Vref0.

The voltage division ratio α is determined from the ratio of theresistance value between the node Nt1 and the ground voltage Vss to theresistance value between the node Nt2 and the ground voltage Vss, whichare set according to the input to the tuning input portion 231 a.

Thus, the reference voltage Vref is not directly programmed, but thevoltage division ratio α for the input voltage to the operationalamplifier 234 is programmed, whereby the response property and noiseresistance of the reference voltage Vref can be improved.

The tuning input portion 231 a includes sets of a fuse element servingas a program element and a transfer gate. These sets are provided inparallel with the transistors 241 to 243, respectively. For example, atransfer gate TGtl and a fuse element 251, which are connected in serieswith each other, are provided in parallel with the transistor 241. Atransfer gate TGt2 and a fuse element 252, which are connected in serieswith each other, are provided in parallel with the transistor 242.Similarly, a transfer gate TGt3 and a fuse element 253, which areconnected in series with each other, are provided in parallel with thetransistor 243.

The fuses can be blown by radiating the laser light from the outsidedirectly to the fuse elements 251 to 253, or by applying a high voltagesignal from the outside through respective blow input nodes 281 to 283.

The tuning input portion 231 a further includes an input terminal 270for receiving a control signal TT that is activated upon conducting thetuning testing of the data write current, input terminals 271 to 273 forreceiving tuning test signals TV1 to TV3, respectively, a logic gate 261for controlling turning ON/OFF of the transfer gate TGt1 according tothe respective levels of the control signal TT and tuning test signalTV1, a logic gate 262 for controlling turning ON/OFF of the transfergate TGt2 according to the respective levels of the control signal TTand tuning test signal TV2, and a logic gate 263 for controlling turningON/OFF of the transfer gate TGt3 according to the respective levels ofthe control signal TT and tuning test signal TV3.

In the normal operation, the control signal TT is inactivated to Llevel. Therefore, the respective output signals of the logic gates 261to 263 are set to H level. In response to this, the transfer gates TGt1to TGt3 are all turned ON. Thus, the voltage division ratio a isdetermined whether the fuse elements 251 to 253 have been blown or not.

In the tuning input portion 231 a, the fuse-blown state can be simulatedby setting the output signal of the logic gate 261 to 263 to L level bythe input signal to the input terminal 270 to 273 so as to turn OFF thecorresponding transfer gate TGt1, TGt2, TGt3.

For example, in the case where the tuning test is conducted with thecontrol signal TT activated (to H level), the transfer gate TGt1 can beturned OFF by activating the tuning test signal TV1 to H level. Thus,the state equivalent to that in which the fuse element 251 has beenblown can be obtained.

Similarly, the fuse-blown state can also be simulated for the fuseelements 252 and 253.

Accordingly, the voltage division ratio a is changed with the controlsignal TT and the tuning test signals TV1 to TV3 that are input to therespective input terminals 270 to 273, so that the reference voltageVref for adjusting the data write current can be set in a variablemanner.

Therefore, in the tuning test, the voltage division ratio α is adjustedreversibly without actually blowing any fuse, whereby the adjustmenttest of the data write current amount for appropriately ensuring thedata write margin can be facilitated.

After the tuning test is completed, the fuse element is actually blownaccording to the test result. Thus, the reference voltage Vref forobtaining an appropriate data write current can be programmed to thetuning input portion 231 a in a non-volatile manner. As a result, thedata write current adjustment circuit 230 produces a programmed,appropriate reference voltage Vref in the normal operation. Therefore,the manufacturing variation in magnetic characteristics of the MTJmemory cells is compensated for, and the data write operation in thenormal operation can be conducted.

Note that FIG. 14 shows the structure including the reference voltageexternal input terminals 202 (212) and 204 (214) for receiving theexternal reference voltage, as well as the transfer gates TGf1 (TGf3)and TGf2 (TGf4). However, these elements may be omitted so that thereference voltage Vref is directly applied to the gate of the transistor153 (34). In this case as well, the tuning test of the data writecurrent can be conducted.

Such a structure enables the tuning test to be conducted merely byinputting a digital signal. That is, the tuning testing can be conductedmore efficiently as compared to the respective structures of the datawrite current adjustment circuits 200 and 210 shown in FIGS. 12 and 13.Moreover, this structure eliminates the need to conduct the adjustmentcorresponding to the output voltage adjustment of the internal referencevoltage generation circuits 206 and 216 included in the data writecurrent adjustment circuits 200 and 210, thereby reducing the load foradjustment.

Note that the number of transistors for setting the voltage divisionratio α is not limited to that in the example shown in FIG. 13, but anyplurality of transistors can be provided. In this case, the level of thereference voltage Vref can be set more finely by providing similarlycontrolled sets of transfer gates and fuse elements as well as controlsignal input terminals in parallel with the plurality of transistorsserving as resistive elements.

FIG. 14 exemplarily shows the structure using as program elements thefuse elements that are disconnected after blow input. However, so-calledanti-fuse elements that are rendered conductive after blow input mayalternatively be used. In this case, the same effects can be obtained byproviding the transfer gates (TGt1 to TGt3 in FIG. 14) for conductingthe tuning test in parallel with the respective anti-fuse elements.

Note that the adjustment of the data write current as described in thesecond embodiment and the modification thereof can be applied not onlyto the MRAM device for conducting the data read operation through theread gate as described in the first embodiment and the modificationsthereof, but also to an MRAM device having a general structure.

FIG. 15 shows an example of the structure of the MRAM device forconducting the data read operation without using the read gate.

The structure of FIG. 15 is different from that of FIG. 2 in that columnselection gates CSG1 to CSGm are provided corresponding to therespective memory cell columns. Each column selection gate couples acorresponding bit line pair BLP to the data I/O line pair DI/OPaccording to the column selection result. For example, the columnselection gate CSG1 couples the data I/O lines IO and /IO of the dataI/O line pair DI/OP to the bit lines BL1 and /BL1 of the correspondingbit line pair BLP1, respectively, according to the voltage on the columnselection line CSL1.

The data write current ±Iw can be supplied to the data I/O line pairDI/OP by the data write circuit 51 b described in connection with FIG.10. The data write current adjustment circuit 200 or 230 shown in FIGS.12 and 14 is provided in order to adjust the current amount of thecurrent source 153 in the data write current supply circuit 52 includedin the data write circuit 51 b. Thus, the adjustment of the data writecurrent can be conducted in the same manner.

The data write current Ip is supplied to the write word line WWL by theword line driver 30. By applying the structure described in connectionwith FIG. 13 to the word line driver 30, the adjustment of the datawrite current can be conducted in the same manner as that of the secondembodiment.

In the MRAM device having the structure of FIG. 15, a data read circuit55d must supply the sense current Is in the data read operation.

The data read circuit 55 d includes current sources 161 and 162 forreceiving the power supply voltage Vcc to supply a constant current torespective internal nodes Ns1 and Ns2, an N-type MOS transistor 163electrically coupled between the internal node Ns1 and a node Nr1, anN-type MOS transistor 164 electrically coupled between the internal nodeNs2 and a node Nr2, and an amplifier 165 for amplifying the voltagelevel difference between the internal nodes Ns1 and Ns2 so as to outputread data DOUT.

The transistors 163 and 164 receive a reference voltage Vrr at theirgates. The respective current amounts supplied from the current sources161 and 162 as well as the reference voltage Vrr are set according tothe amount of the sense current Is. Resistances 166 and 167 are providedin order to pull down the internal nodes Ns1 and Ns2 to the groundvoltage Vss, respectively. The nodes Nr1 and Nr2 are coupled to the dataI/O lines IO and /IO, respectively.

With such a structure, the data read circuit 55d supplies the sensecurrent Is to each of the data I/O lines IO and /IO in the data readoperation. The read data DOUT is output according to the respectivevoltage changes produced on the data I/O lines IO and /IO correspondingto the storage data level in the MTJ memory cell connected theretothrough the column selection gate and the bit line pair.

Third Embodiment

In the third embodiment is described the structure in which the bitlines BL and write word lines WWL receiving the data write current areformed in a plurality of wiring layers.

FIG. 16 shows the bit line arrangement according to the third embodimentof the present invention.

Referring to FIG. 16, the data write and read operations to and from thememory array 10 are conducted through the data I/O line pair DI/OP bythe data write circuit 51 b and the data read circuit 55 d,respectively, based on the same structure as that of FIG. 15.

The bit lines BL1 to BLm, /BL1 to /BLm forming the bit line pairs BLP1to BLPm, column selection gates CSG1 to CSGm, and column selection linesCSL1 to CSLm are provided corresponding to the respective memory cellcolumns.

The bit lines BL1 to BLm are formed in a wiling layer different fromthat of the bit lines /BL1 to /BLm. For example, the bit lines BL1 toBLm are each formed in a metal wiring layer M3, whereas the bit lines/BL1 to /BLm are each formed in a metal wiling layer M4.

Each memory cell MC is coupled to one bit line BL of the correspondingbit line pair. Each dummy memory cell DMC is coupled to the other bitline /BL of the corresponding bit line pair.

The read/write control circuit 60 includes equalizing transistors 62-1to 62-m provided corresponding to the respective memory cell columns.The equalizing transistor 62 short-circuits the bit lines BL and /BLformed in different metal wiring layers, in response to a bit lineequalizing signal BLEQ. The bit line equalizing signal BLEQ isactivated/inactivated in the same manner as that described in the firstembodiment.

Accordingly, in the data write operation, the data write current +Iw forthe bit line pair BLP is supplied to the bit lines BL and /BL in theselected memory cell column so as to flow in the different directions asa reciprocating current. Thus, the structure of the data write circuit51 b including the data write current supply circuit 52 can be appliedas in the case of the first embodiment.

As a result, like the first embodiment, a return path of the data writecurrent ±Iw can be provided by the equalizing transistor 62. Therefore,the structure for sinking the data write current need not be provided inthe read/write control circuit 60, achieving reduction in layout area ofthe peripheral circuitry.

FIG. 17 shows a first example of the bit line arrangement according tothe third embodiment.

Referring to FIG. 17, the write word line WWL is formed in a metalwiring layer M2. The bit line pair BLP has the bit line BL formed in themetal wiling layer M3 and the bit line /BL formed in the metal wilinglayer M4. The bit lines BL and /BL are thus formed in the differentmetal wiring layers so as to interpose the magnetic tunnel junction MTJtherebetween in the vertical direction. As described before, the bitlines BL and /BL are electrically coupled to each other through theequalizing transistor 62 at the end of the memory array 10, so that thedata write current flows therethrough.

Accordingly, the data write current ±Iw in the data write operationflows through the bit lines BL and /BL in the different directions.Thus, in the magnetic tunnel junction MTJ, the data write magneticfields produced by the data write current ±Iw act in such a directionthat the respective magnetic fields produced by the bit lines BL and /BLenhance each other. Accordingly, the data write current ±Iw in the datawrite operation can be reduced. As a result, reduced current consumptionof the MRAM device, improved reliability resulting from a reduced bitline current density, and reduced magnetic field noise in the data writeoperation can be achieved.

On the contrary, in the peripheral portion including other memory cells,the respective magnetic fields produced by the bit lines BL and /BL actin such a direction that cancels each other. As a result, the magneticfield noise in the data write operation can further be suppressed.

FIG. 18 shows a second example of the bit line arrangement according tothe third embodiment.

Referring to FIG. 18, the write word line WWL is provided in the metalwiling layer M3. The bit lines BL and /BL are provided in the differentmetal wiling layers M2 and M4 so as to interpose the magnetic tunneljunction MTJ therebetween in the vertical direction. In this structureas well, the magnetic fields produced by the data write current ±Iw actin the same direction as that of FIG. 17. Thus, the same effects asthose obtained with the structure of FIG. 17 can be obtained.

Referring back to FIG. 16, in the third embodiment, an external powersupply voltage Ext.Vcc to the MRAM device 1 is supplied directly to thedata write circuit 51 b and the word line driver 30 for activating thewrite word line WWL, i.e., the components for supplying the data writecurrent in the data write operation.

The MRAM device 1 further includes a voltage down converter (VDC) 7 fordown-converting the external power supply voltage Ext.Vcc to produce aninternal power supply voltage Int.Vcc.

The internal power supply voltage Int.Vcc produced by the voltage downconverter 7 is supplied to the internal circuitry for conducting thedata read operation and address processing, such as the data readcircuit 55d, column decoder 25, control circuit 5 and row decoder 20.

With such a structure, the data write circuit for supplying a relativelylarge data write current ±Iw as well as the word line driver forsupplying the data write current Ip to the write word line WWL is drivenwith the external power supply voltage Ext.Vcc in the data writeoperation. As a result, these data write currents can be suppliedquickly.

On the other hand, the internal circuitry other than the circuitry forsupplying the data write current is driven with the down-convertedinternal power supply voltage Int.Vcc. As a result, power consumption inthe internal circuitry can be reduced, as well as the reliabilitycorresponding to the shrinking of the device for improved integrationcan be ensured.

First Modification of Third Embodiment

Referring to FIG. 19, in the bit line arrangement according to the firstmodification of the third embodiment, the bit lines BL and /BL of eachbit line pair BLP are provided in the metal wiling layers M3 and M4 soas to cross each other in a region CRS in the memory array 10.

More specifically, in the region located on the left side of the regionCRS, the bit lines BL and /BL are respectively formed from the wiringsprovided in the metal wiling layers M3 and M4. In the region located onthe light side of the region CRS, however, the bit lines BL and /BL arerespectively formed from the wirings provided in the metal wiling layersM4 and M3.

The wirings corresponding to the bit line BL, which are formed in themetal wiling layers M3 and M4, are coupled to each other in the regionCRS. Similarly, the wirings corresponding to the bit line /BL, which areformed in the metal wiling layers M3 and M4, are coupled to each otherin the region CRS.

The bit lines BL and /BL are coupled to the memory cells MC in one ofthe metal wiling layers. In FIG. 18, the bit lines BL and /BL arecoupled to the memory cells MC in the lower metal wiling layer M3structurally having a smaller distance to the magnetic tunnel junctionMTJ.

Thus, each of the memory cells MC in the same memory cell column iscoupled to either the bit line BL or /BL. Accordingly, a dummy memorycells DMC coupled to the bit line BL and a dummy memory cell DMC coupledto the bit line /BL are provided in each memory cell column. A dummyread word line DRWL1 is provided in common to the dummy memory cells DMCcoupled to the respective bit lines BL. Similarly, a dummy read wordline DRWL2 is provided in common to the dummy memory cells DMC coupledto the respective bit lines /BL.

The equalizing transistors 62-1 to 62-m are provided corresponding tothe respective memory cell columns, for coupling the bit lines BL and/BL of the corresponding bit line pair to each other in response to thebit line equalizing signal BLEQ.

With such a structure, a reciprocating current turning around at theequalizing transistor 62 flows through the bit lines BL and /BL in theselected memory cell column, whereby the data write operation based onthe folded bit line structure can be conducted.

Thus, in the bit line arrangement of FIG. 19, the same number of memorycells can be coupled to each of the bit lines BL and /BL of each bitline pair. Therefore, the imbalance of the RC load between the bit linesBL and /BL of the same bit line pair BLP can be corrected. Moreover,since the data read operation based on the folded bit line structure canbe conducted using the dummy memory cells, the data read operationmargin can further be improved.

Since the structure and the basic operation in reading and writing thedata are otherwise the same as those of FIG. 15, detailed descriptionthereof will not be repeated.

Second Modification of Third Embodiment

Hereinafter, the structure in which the write word lines WWL are formedin a plurality of metal wiring layers will be described.

FIG. 20 is a structural diagram illustrating the arrangement of thewrite word lines WWL according to the second modification of the thirdembodiment.

Referring to FIG. 20, the write word line WWL include a sub write wordline WWL1 formed in the metal wiling layer M2 and a sub write word lineWWLu formed in the metal wiring layer M4. The sub write word lines WWL1and WWLu are provided so as to interpose the magnetic tunnel junctionMTJ therebetween in the vertical direction.

FIGS. 21A and 21B are conceptual diagrams illustrating coupling betweenthe sub write word lines forming the same write word line WWL.

Referring to FIGS. 21A and 21B, the sub write word lines WWLu and WWL1forming the same write word line WWL are electrically coupled to eachother at the end of the memory array 10. This enables the data writecurrent Ip to be supplied as a reciprocating current using the sub writeword lines WWLu and WWL1.

In FIG. 21A, the sub write word lines WWLu and WWL1 are electricallycoupled to each other through a metal wiring 145 provided in a throughhole 144.

As shown in FIG. 21B, a write word line current control switch TSWformed from a MOS transistor electrically coupled between the sub writeword lines WWLu and WWL1 may be provided in order to short-circuit thesub write word lines WWLu and WWL1.

Such a structure enables the data write current Ip to be supplied to thesub write word lines WWLu and WWL1 of the same write word line WWL inthe opposite directions as a reciprocating current.

Referring back to FIG. 20, by applying the data write current Ip to thesub write word lines WWL1 and WWLu in the opposite directions, therespective data write magnetic fields produced at the magnetic tunneljunction MTJ by the sub write word lines WWLu and WWL1 act in the samedirection, as in the case of FIGS. 16 and 17.

In the peripheral portion including other memory cells, the respectivemagnetic fields produced by the sub write word lines WWLu and WWL1 actin such a direction that cancels each other. Thus, with the same currentvalue, a larger data write magnetic field can be applied to the magnetictunnel junction MTJ. As a result, the amount of data write currentrequired to produce a desired data write magnetic field is reduced.

Thus, reduced current consumption of the MRAM device, improved operationreliability resulting from a reduced current density of the write wordline WWL, and reduced magnetic field noise in the data write operationcan be realized simultaneously.

Third Modification of Third Embodiment

Referring to FIG. 22, in the structure according to the thirdmodification of the third embodiment, the row decoder 20 and write worddrivers WWD1 to WWDn included in the word line driver 30 are provided atone end of the memory array 10 along the row direction. The write worddrivers WWD1 to WWDn are provided corresponding to the respective writeword lines WWL1 to WWLn, for activating the corresponding write wordline WWL according to the decode result of the row decoder 20 so as tosupply the data write current Ip thereto.

The write word lines WWL are arranged according to the structure shownin FIGS. 20 and 21A. More specifically, the sub write word lines WWLuand WWL1 forming the same write word line WWL are electrically coupledto each other at the other end of the memory array 10 through the metalwiring 145 in the through hole.

The write word drivers WWD1 to WWDn supply the data write current Ip toone sub write word line WWLu of the corresponding write word line WWL.The other sub write word line WWL1 forming the same write word line WWLis coupled to the ground voltage Vss at one end (on the side of thewrite word driver WWD) of the memory array 10.

Such a structure enables the data write current Ip for the data writeoperation to be supplied to the write word line WWL corresponding to theselected memory cell column as a reciprocating current using the subwrite word lines WWLu and WWL1. Note that the connection between the subwrite word line WWLu, WWL1 and the write word driver WWD and groundvoltage Vss may be switched so that the sub write word line WWL1 iscoupled to the write word driver WWD and the sub write word line WWLu iscoupled to the ground voltage Vss.

Fourth Modification of Third Embodiment

Referring to FIG. 23, in the structure according to the fourthmodification of the third embodiment, the write word drivers WWDcorresponding to the respective write word lines WWL are providedseparately at both ends of the memory array 10. Accordingly, the rowdecoder is also provided separately as a row decoder 20 a for activatingthe write word drivers corresponding to the odd rows and a row decoder20 b for controlling the write word drivers corresponding to the evenrows.

As described before, the write word driver WWD includes a transistor forsupplying the data write current Ip, requiring a relatively large size.Accordingly, providing the write word drivers WWD separately on bothsides of the memory array allows the layout pitch corresponding to tworows to be utilized for each write word driver WWD. This improves theintegration of the write word lines WWL in the row direction, allowingfor efficient reduction in area of the memory array 10.

Since the structure and operation are otherwise the same as those ofFIG. 22, detailed description thereof will not be repeated.

Fifth Modification of Third Embodiment

Referring to FIG. 24, in the structure according to the fifthmodification of the third embodiment, the sub write word lines WWLu toWWL1 forming the same write word line WWL are electrically coupled toeach other by a corresponding write word line current control switch TSWat one end (on the side of the row decoder 20) of the memory array 10.The write word line current control switches TSW are providedcorresponding to the respective memory cell rows.

FIG. 24 exemplarily shows the write word line current control switchesTSW1 and TSW2 corresponding to the write word lines WWL1 and WWL2,respectively. The write word line current control switch TSW is turnedON under the control of the row decoder 20 in response to selection ofthe corresponding memory cell row.

The sub write word lines WWLu and WWL1 forming the same write word lineWWL are respectively coupled to the power supply voltage Vcc and theground voltage Vss at the other end of the memory array 10. Accordingly,the write word line current control switch TSW is turned ON based on therow selection result, whereby the reciprocating data write current Ipcan be supplied to the sub write word lines WWLu and WWL1 of thecorresponding write word line WWL. Thus, the same effects as those ofthe third and fourth modifications of the third embodiment can beobtained.

During the OFF period of the corresponding write word line currentcontrol switch TSW, the sub write word lines WWLu and WWL1 arerespectively set to the power supply voltage Vcc and the ground voltageVss. Accordingly, the voltage on the write word line WWL can be restoredrapidly to the stand-by state or non-selected state after the operationof selecting the write word line WWL is completed.

FIG. 24 exemplarily shows the structure in which the sub write wordlines WWLu and WWL1 are respectively coupled to the power supply voltageVcc and the ground voltage Vss at the other end of the memory array 10.However, this connection may be switched such that the sub write wordlines WWLu and WWL1 are respectively coupled to the ground voltage Vssand the power supply voltage Vcc.

More specifically, since the reciprocating data write current Ip issupplied in the data write operation, the write word line WWL isincreased in length. However, the write word line WWL is divided intothe sub write word lines WWLu and WWL1, which are restored to therespective prescribed voltage levels. Such a structure enables the writeword line WWL to be restored rapidly to the stand-by state or thenon-selected state while obtaining the effects resulting from supplyingthe data write current as a reciprocating current.

Note that, in the third to fifth modifications of the third embodiment,at least one of the dummy write word lines DWWL1, DWWL2 and write worddrivers DWWD1, DWWD2 and the write word line current control switchesDTSW1, DTSW2 is provided also for the dummy memory cells MC thatoriginally do not relate to the data write operation. The dummy writeword lines DWWL1, DWWL2, the write word drivers DWWD1, DWWD2, and thewrite word line current control switches DTSW1, DTSW2 each has the samestructure as that provided for the memory cell MC.

However, since the data write current need not be supplied to the dummymemory cells DMC, the input of the write word drivers DWWD1 and DWWD2corresponding to the dummy memory cells is fixed to the power supplyvoltage Vcc. Accordingly, the dummy write word line DWWL1, DWWL2 isalways retained in the inactive state (ground voltage Vss), and acurrent is not applied thereto. Moreover, the gate of the N-type MOStransistor forming the corresponding write word line current controlswitch DTSW is fixed to the ground voltage Vss, so that the N-type MOStransistor is retained in the OFF state.

Providing the write word lines WWL in the memory array 10 except for theregion corresponding to the dummy memory cells DMC causes lack incontinuity in terms of the shape. This may possibly result in defectiveshape during production of the MRAM device. In order to avoid such aproblem, the write word lines, write word drivers, and peripheralcircuitry thereof (write word line current control switches TSW in FIG.24) each having the same structure as that provided for the regularmemory cells MC can be provided also for the dummy memory cells DMC forwhich the data write operation is not required.

Note that it is also possible to combine the arrangement of the bitlines and write word lines according to the third embodiment and themodifications thereof with each or both of the first and secondembodiments. In this case, the data write circuit and the data readcircuit need only be structured as described in the first and secondembodiments and the modifications thereof.

Fourth Embodiment

Referring to FIG. 25, an MTJ memory cell MCD according to the fourthembodiment includes a magnetic tunnel junction MTJ and an access diodeDM, as in the structure of FIG. 90. The MTJ memory cell MCD is differentfrom that of FIG. 90 in that the read word line RWL and the write wordline WWL are separately provided. The bit line BL extends in such adirection that crosses the write word lines WWL and the read word lineRWL, and is electrically coupled to the magnetic tunnel junction MTJ.

The access diode DM is coupled between the magnetic tunnel junction MTJand the read word line RWL. Herein, the direction from the magnetictunnel junction MTJ toward the read word line RWL is a forwarddirection. The write word line WWL is provided near the magnetic tunneljunction MTJ without being connected to the bit line BL, read word lineRWL and access diode DM.

Referring to FIG. 26, an N-type region (N-well, n⁺ diffusion region, orthe like) NWL formed at the semiconductor main substrate SUB correspondsto the cathode of the access diode DM. In the case where the MTJ memorycells are arranged in rows and columns on the semiconductor substrate,the N-type regions NWL for the MTJ memory cells in the same row may beelectrically coupled to each other. Thus, the coupling between theaccess diode DM and the read word line RWL as shown in FIG. 25 can beimplemented without providing the read word line RWL.

A P-type region PAR formed at the N-type region NWL corresponds to theanode of the access diode DM. The P-type region PAR is electricallycoupled to the magnetic tunnel junction MTJ through a barrier metal 140and a metal film 150.

The write word line WWL and the bit line BL are respectively provided inthe metal wiring layers M1 and M2. The bit line BL is coupled to themagnetic tunnel junction MTJ.

FIG. 27 is a timing chart illustrating the read and write operationsfrom and to the MTJ memory cell MCD.

Referring to FIG. 27, in the data write operation, the voltage on theread word line RWL, i.e., the N-type region NWL, is set to H level(power supply voltage Vcc). In the data read operation, no current flowthrough the read word line RWL.

The power supply voltage Vcc is applied to the write word line WWLcorresponding to the selected memory cell, so that the data writecurrent Ip flows therethrough. According to the write data level, thebit line BL is set to the power supply voltage Vcc at its one end and tothe ground voltage Vss at the other end. Thus, the data write current±Iw corresponding to the write data level can be supplied to the bitline BL.

With the data write currents Ip and ±Iw thus supplied, the data iswritten to the MTJ memory cell. In this case, the read word line RWL isset to the power supply voltage Vcc, so that the access diode DM isreliably turned OFF in the data write operation. As a result, the datawrite operation can be conducted more stably as compared to the case ofthe MTJ memory cell shown in FIG. 90.

Hereinafter, the data read operation will be described.

Before the data read operation, the bit lines BL are precharged to theground voltage Vss.

The read word line RWL corresponding to the memory cell MCD to be readis driven to the active state (L level: ground voltage Vss) in the dataread operation. In response to this, the access diode DM is biased inthe forward direction. Thus, the sense current Is is supplied to a pathformed from the bit line BL, magnetic tunnel junction MTJ, access diodeDM and read word line RWL (ground voltage Vss), enabling the data readoperation.

More specifically, a voltage change produced on the bit line BL isamplified with the sense amplifier Is, so that the storage data in themagnetic tunnel junction MTJ can be read.

Note that, as shown in FIG. 26, the distance between the bit line BL andthe magnetic tunnel junction MTJ is smaller than that between the writeword line WWL and the magnetic tunnel junction MTJ. Therefore, with thecurrent amount being the same, the magnetic field produced by the datawrite current flowing through the bit line BL is larger than thatproduced by the data write current flowing though the write word lineWWL.

In order to apply the data write magnetic fields of approximately thesame strength to the magnetic tunnel junction MTJ, a larger data writecurrent must be supplied to the write word line WWL than to the bit lineBL. The bit line BL and the write word line WWL are formed in the metalwiling layers in order to reduce the electrical resistance value.However, an excessive current density in the wirings may possibly causedisconnection or short-circuit of the wirings due to theelectromigration phenomenon, thereby possibly degrading the operationreliability. It is therefore desirable to suppress the current densityof the wirings receiving the data write current.

Accordingly, in the case where the MTJ memory cell MCD shown in FIG. 25is provided on the semiconductor substrate, the cross sectional area ofthe write word line WWL is made larger than that of the bit line BLlocated closer to the magnetic tunnel junction MTJ, in order to suppressthe current density of the write word line WWL to which a larger datawrite current must be supplied. Thus, improved reliability of the MRAMdevice can be achieved.

For the improved reliability, it is also effective to form a metalwiring located farther from the magnetic tunnel junction MTJ and thusrequiring a larger data write current to be supplied thereto (i.e., thewrite word line WWL in FIG. 26), from a highlyelectromigration-resistant material. For example, in the case where theother metal wirings are formed from an aluminum alloy (Al alloy), themetal wirings that may be subjected to electromigration may be formedfrom copper (Cu).

FIG. 28 is a conceptual diagram showing the memory array structurehaving the MTJ memory cells MCD arranged in rows and columns.

Referring to FIG. 28, with the MTJ memory cells arranged in rows andcolumns on the semiconductor substrate, a highly integrated MRAM devicecan be realized. FIG. 28 shows the case where the MTJ memory cells MCDare arranged in n rows by m columns.

As described before, the bit line BL, write word line WWL and read wordline RWL must be provided for each MTJ memory cell MCD. Accordingly, nwrite word lines WWL1 to WWLn, n read word lines RWL1 to RWLn, and m bitlines BL1 to BLm are provided for the MTJ memory cells arranged in nrows by m columns.

FIG. 29 shows the memory array structure in which the MTJ memory cellsMCD arranged in rows and columns share the write word lines WWL.

Referring to FIG. 29, the read word lines RWL and write word lines WWLprovided for the MTJ memory cells MCD having the structure of FIG. 25extend in the row direction. Each write word line WWL is shared betweenadjacent memory cells.

For example, the MTJ memory cell coupled to the read word line RWL1 andthe MTJ memory cell coupled to the read word line RWL2 share the samewrite word line WWL1.

Such sharing of the write word lines WWL can reduce the number of writeword lines WWL in the whole memory array. Thus, improved integration ofthe MTJ memory cells in the memory array as well as reduced chip areacan be achieved.

Such a reduced number of write word lines WWL also ensures the wilingpitch of the write word lines WWL in the metal wiling layer M1 shown inFIG. 26. Accordingly, an increased wiling width of the write word lineWWL can be readily obtained. This makes it easy to make the crosssectional area of the write word line WWL larger that of the bit line BLlocated closer to the magnetic tunnel junction MTJ. As a result, theelectromigration can be suppressed, whereby improved reliability of theMRAM device can be readily achieved.

Moreover, the MTJ memory cells MCD according to the fourth embodimentmay be used in the first to third embodiments as memory cells MCarranged in the memory array 10.

Modification of Fourth Embodiment

Such sharing of the wirings can be applied to the conventional MTJmemory cell having the structure shown in FIG. 90.

FIG. 30 shows the arrangement of the MTJ memory cells according to themodification of the fourth embodiment.

FIG. 30 shows a memory array integrating MTJ memory cells MCD′ havingthe structure shown in FIG. 90.

Referring to FIG. 30, in the memory array having the MTJ memory cellsMCD′ arranged in rows and columns according to the modification of thefourth embodiment, adjacent memory cell MCD′ in the column directionshare the same word line WL. For example, the memory cell MCD′ of thefirst memory cell row and the memory cell MCD′ of the second memory cellrow share the same word line WL1.

Such a structure reduces the number of word lines WL in the entirememory array, whereby improved integration of the MTJ memory cells aswell as reduced chip area can be achieved.

Referring back to FIG. 91, in the MTJ memory cell of FIG. 90 as well,the distance between the word line WL and the magnetic tunnel junctionMTJ is larger than that between the bit line BL and the magnetic tunneljunction MTJ. Accordingly, a larger data write current must be suppliedto the word line WL. In order to ensure the operation reliability, it isimportant to reduce the current density on the word line WL in such anMTJ memory cell.

In the modification of the fourth embodiment, the wiring pitch of theword lines WL requiring a larger data write current can be readilyensured. Accordingly, the current density on the word line WL issuppressed, whereby the improved reliability of the MRAM device can beachieved. As described in the fourth embodiment, the operationreliability of the MRAM device can further be improved by using a higherelectromigration-resistant material to form the wiling to which a largerdata rite current must be supplied.

Fifth Embodiment

In the fifth and the following embodiments, improved integration of thememory array is described for the case where the read word line RWL andthe write word line WWL extend in different directions.

Referring to FIG. 31, in an MRAM device 2 according to the fifthembodiment of the present invention, the read word lines RWL and thewrite word lines WWL respectively extend in the row and columndirections on the memory array 10.

The bit lines are correspondingly divided into read bit lines RBL andwrite bit lines WBL, so that the read bit lines RBL and the write bitlines WBL respectively extend in the column and row directions on thememory array 10.

Accordingly, the MRAM device 2 is different from the MRAM device 1 ofFIG. 1 in that the word line driver 30 is divided into a read word linedriver 30 r and a write word line driver 30 w.

The read/write control circuits 50, 60 are also divided into writecontrol circuits 50 w, 60 w provided adjacent to the memory array 10 inthe row direction, and a read control circuit 50 r.

Since the structure and operation are otherwise the same as those of theMRAM device 1, detailed description thereof will not be repeated.

Referring to FIG. 32, in the fifth embodiment, the read word line RWL,Write word line WWL, write bit line WBL and read bit line RBL areprovided for the MTJ memory cell having the magnetic tunnel junction MTJand access transistor ATR. A MOS transistor, which is a field effecttransistor formed on the semiconductor substrate SUB, is typically usedfor the access transistor ATR.

The access transistor ATR has its gate coupled to the read word lineRWL. The access transistor ATR is turned ON (actuated) in response toactivation of the read word line RWL to the selected state (H level:power supply voltage Vcc), forming a current path including the magnetictunnel junction MTJ. On the other hand, when the read word line RWL isinactivated to the non-selected state (L level: ground voltage Vss), theaccess transistor ATR is turned OFF. Therefore, the current pathincluding the magnetic tunnel junction MTJ is not formed.

Thus, by providing the read word line RWL and the write word line WWLextending perpendicularly to each other, the read word line driver 30 rand the write word line driver 30 w can be provided separately.

The write word line WWL and the write bit line WBL extend perpendicularto each other near the magnetic tunnel junction MTJ.

The write word line WWL can be provided independently without beingcoupled to other portions of the MTJ memory cell. Accordingly, the writeword line WWL can be arranged for improved magnetic coupling with themagnetic tunnel junction MTJ. Thus, the data write current Ip flowingthrough the write word line WWL can be suppressed.

Since the respective activation of the read word line RWL and the writeword line WWL is controlled independently in the data read and writeoperations, their respective drivers can be originally designed asindependent drivers. Accordingly, the write word line driver 30 w andthe read word line driver 30 r each having a reduced size can beseparately provided in different regions adjacent to the memory array10. As a result, the freedom of layout is improved, whereby the layoutarea, i.e., the chip area of the MRAM device, can be reduced.

The magnetic tunnel junction MTJ is electrically coupled between theread bit line RBL and the access transistor ATR. Accordingly, in thedata read operation, the voltage level on the write bit line WBL thatrequires no current supply is set to the ground voltage Vss. As aresult, a current path is formed by the read bit line RBL, magnetictunnel junction MTJ, access transistor ATR and write bit line WBL(ground voltage Vss) in response to turning-ON of the access transistorATR. In response to the sense current Is supplied to this current path,a voltage change corresponding to the storage data level in the magnetictunnel junction MTJ is produced on the read bit line RBL, whereby thestorage data can be read.

In the data write operation, the data write current is supplied to eachof the write word line WWL and the write bit line WBL. When the sum ofthe magnetic fields produced by these data write currents reaches afixed magnetic field, i.e., the region beyond the asteroidcharacteristic line shown in FIG. 86, the storage data is written to themagnetic tunnel junction MTJ.

Hereinafter, the data write and read operations to and from the MTJmemory cell according to the fifth embodiment will be described withreference to FIG. 33.

First, the data write operation will be described.

According to the column selection result of the column decoder 25, thewrite word line driver 30 w drives the voltage on the write word lineWWL corresponding to the selected column to the selected state (Hlevel). In the non-selected columns, the voltage levels on the writeword lines WWL are retained in the non-selected state (L level). Sinceeach write word line WWL is coupled to the ground voltage Vss by theword line current control circuit 40, the data write current Ip flowsthrough the write word line WWL of the selected column.

In the data write operation, the read word lines RWL are retained in thenon-selected state (L level). In the data write operation, the readcontrol circuit 50 r does not supply the sense current Is, butprecharges the read bit lines RBL to the high voltage state (Vcc). Sincethe access transistors ATR are retained in the OFF state, no currentflows through the read bit lines RBL in the data write operation.

The write control circuits 50 w and 60 w control the voltage on thewrite bit line WBL at both ends of the memory array 10, therebyproducing a data write current in the direction corresponding to thelevel of the write data DIN.

For example, in order to write the storage data “1”, the bit linevoltage on the side of the write control circuit 60 w is set to the highvoltage state (power supply voltage Vcc), and the bit line voltage onthe opposite side, i.e., on the side of the write control circuit 50 w,is set to the low voltage state (ground voltage Vss). As a result, thedata write current +Iw flows through the write bit line WBL from thewrite control circuit 60 w toward 50 w.

In order to write the storage data “0”, the bit line voltages on theside of the write control circuits 50 w and 60 w are respectively set tothe high and low voltage states, whereby the data write current −Iwflows through the write bit line WBL from the write control circuit 50 wtoward 60 w. At this time, the data write current ±Iw is selectivelyapplied to the write bit line WBL corresponding to the selected row,according to the row selection result of the row decoder 20.

By setting the directions of the data write currents Ip and ±Iw in thisway, one of the data write currents +Iw and −Iw of the oppositedirections is selected according to the storage data level “1” or “0” tobe written, and the data write current Ip on the write word line WWL canbe made to flow in the fixed direction regardless of the data level.Thus, the data write current Ip flowing through the write word line WWLcan be always kept in the fixed direction. As a result, the structure ofthe word line current control circuit 40 can be simplified, as describedbefore.

Next, the data read operation will be described.

In the data read operation, the write word lines WWL are retained in thenon-selected state (L level), and the voltage level thereof is fixed tothe ground voltage Vss by the word line current control circuit 40. Inthe data read operation, the write control circuits 50 w and 60 wdiscontinue supply of the data write current to the write bit line WBL,and set the write bit lines WBL to the ground voltage Vss.

The read word line driver 30 r drives the read word line RWLcorresponding to the selected row to the selected state (H level),according to the row selection result of the row decoder 20. In thenon-selected rows, the voltage levels on the read word lines RWL areretained in the non-selected state (L level). In the data readoperation, the read control circuit 50 r supplies the read bit line RBLof the selected column with a fixed amount of sense current Is forconducting the data read operation. The read bit lines RBL areprecharged to the high voltage state (Vcc) before the data readoperation. Therefore, when the access transistor ATR is turned ON inresponse to activation of the read word line RWL, a current path of thesense current Is is formed within the MTJ memory cell, whereby a voltagechange (drop) corresponding to the storage data is produced on the readbit line RBL.

It is now assumed in FIG. 33 that the fixed magnetic layer FL and thefree magnetic layer VL have the same magnetic field direction when thestorage data level is “1”. In this case, the read bit line RBL has asmall voltage change ΔV1 when the storage data is “1”, and has a voltagechange ΔV2 larger than ΔV1 when the storage data is “0”. The storagedata of the MTJ memory cell can be read by sensing the differencebetween the voltage drops ΔV1 and ΔV2.

In the data write operation, the read bit lines RBL are set to the samevoltage as the precharge voltage for the data read operation, i.e., thepower supply voltage Vcc. This enables the precharging operation for theread data operation to be conducted efficiently, increasing the dataread operation speed. Note that, when the precharge voltage of the readbit lines RBL is set to the ground voltage Vss, the read bit lines RBLneed only be set to the ground voltage Vss in the data write operation.

Similarly, the write bit lines WBL, which must be set to the groundvoltage Vss in the data read operation, can be set to the ground voltageVss after the data write operation, in order to increase the data readspeed.

Referring to FIG. 34, in the MTJ memory cell according to the fifthembodiment, the access transistor ATR is formed in a p-type region PARof the semiconductor substrate SUB. The write bit line WBL is formed ina first metal wiling layer M1 so as to be electrically coupled to one ofthe source/drain regions, i.e., 110, of the access transistor ATR. Theother source/drain region 120 is electrically coupled to the magnetictunnel junction MTJ through a metal wiling provided in the first metalwiling layer Ml, a barrier metal 140 and a metal film 150 formed in acontact hole.

The read bit line RBL is provided in a third metal wiling layer M3 so asto be electrically coupled to the magnetic tunnel junction MTJ. Thewrite word line WWL is provided in a second metal wiring layer M2. Thewrite word line WWL can be independently provided without being coupledto other portions of the MTJ memory cell. Therefore, the write word lineWWL can be arbitrarily arranged so as to enhance the magnetic couplingwith the magnetic tunnel junction MTJ.

With such a structure, the read word line RWL and the write word lineWWL are provided for the MTJ memory cell so as to extend perpendicularlyto each other, and the read word line driver 30 r and write word linedriver 30 w respectively corresponding to the read word line RWL andwrite word line WWL are independently provided. Thus, the freedom oflayout can be improved. Moreover, a word line drive current is preventedfrom being excessively increased in the data read operation, wherebygeneration of undesirable magnetic noise can be prevented.

Referring to FIG. 35, in the memory array 10 according to the fifthembodiment, the memory cells MC having the structure of FIG. 32 arearranged in rows and columns. The read word lines RWL and the write wordlines WWL respectively extend in the row and column directions. The readbit lines RBL and the write bit lines WBL respectively extend in thecolumn and row directions. The read bit lines and the write bit linesare also generally denoted with RBL and WBL, respectively, and aspecific read bit line and write bit line are denoted with, e.g., RBL1and WBL1.

The word line current control circuit 40 couples each write word lineWWL to the ground voltage Vss. Thus, in the data read and writeoperations, the voltage and current on the write word line WWL can becontrolled as shown in FIG. 33.

Adjacent memory cells in the row direction share the read bit line RBL,and adjacent memory cells in the column direction share the write bitline WBL.

For example, the memory cell group of the first and second memory cellcolumns shares the same read bit line RBL1, and the memory cell group ofthe third and fourth memory cell columns shares the same read bit lineRBL2. Moreover, the memory cell group of the second and third memorycell rows shares the write bit line WBL2. In the following memory cellrows and columns as well, the read bit lines RBL and the write bit linesWBL are arranged similarly.

If the data is to be read from or written to a plurality of memory cellsMC of the same read bit line RBL or write bit line WBL, data collisionoccurs. Accordingly, the memory cells MC are arranged alternately.

With such a structure, the pitches of the read bit lines RBL and thewrite bit lines WBL in the memory array 10 can be widened. As a result,the memory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Hereinafter, the peripheral circuitry for supplying the sense current Isand the data write current ±Iw will be described.

Column selection for the data read operation is conducted using the readcolumn selection lines RCSL and the read column selection gates RCSG,both provided corresponding to the respective read bit lines RBL. FIG.35 exemplarily shows the read column selection lines RCSL1, RCSL2 andthe read column selection gates RCSG1, RCSG2, which are providedcorresponding to the respective read bit lines RBL1 and RBL2.

In the data read operation, the column decoder 25 activates one of theplurality of read column selection lines RCSL to the selected state (Hlevel) according to the column selection result.

The read column selection gate RCSG connects a read data line RDL to thecorresponding read bit line RBL according to the voltage on thecorresponding read column selection line RCSL. A data read circuit 55 esupplies the sense current Is to the read data line RDL.

Referring to FIG. 36, the data read circuit 55 e is different from thedata read circuit 55 d of FIG. 15 in that the data read circuit 55 esupplies the sense current Is only to the node Nr1. Accordingly, thetransistor 164 shown in FIG. 15 is eliminated, and the reference voltageVref is applied only to the gate of the transistor 163.

The data read circuit 55 e senses the level of the-read data DOUT basedon the comparison between a voltage drop caused by the sense current Isand a reference voltage drop ΔVr. Provided that the data line has avoltage drop ΔVh when the H-level data is read, and has a voltage dropΔVl when the L-level data is read, ΔVr is set to an intermediate valueof ΔVh and ΔVl.

Accordingly, in the data read circuit 55 e, the resistance value of theresistance 167 is set so that the node Ns2 has a voltage level(Vcc-ΔVr).

Referring back to FIG. 35, the sense current Is is selectively suppliedto the read bit line RBL corresponding to the column selection resultthrough the read column selection gate RCSG.

According to the row selection result, the read word line driver 30 rselectively activates the read word line RWL. Thus, the sense current Iscan be supplied to the MTJ memory cell corresponding to the selectedmemory cell row.

On the other hand, column selection for the data write operation isconducted in response to selective activation of the write word line WWLby the write word line driver 30 w according to the column selectionresult. Each write word line WWL is coupled to the ground voltage Vss inthe word line current control circuit 40.

The write bit lines WBL are provided corresponding to the respectivememory cell rows so as to extend perpendicularly to the write word linesWWL. Accordingly, row selection for the data write operation isconducted using write row selection lines and write row selection gates,which are provided corresponding to the respective write bit lines WBL.

FIG. 35 exemplarily shows the write row selection lines WRSL1, WRSL2 andthe write row selection gates WRSG1, WRSG2, which are providedcorresponding to the write bit lines WBL1, WBL2. Hereinafter, the writerow selection lines and the write row selection gates are also generallydenoted with WRSL and WRSG, respectively.

The write row selection gate WRSG is electrically coupled between thecorresponding write bit line WBL and a write data line WDL, and isturned ON/OFF according to the voltage on the corresponding write rowselection line WRSL.

The read/write control circuit 60 includes bit line current controltransistors provided corresponding to the respective write bit linesWBL. FIG. 35 exemplarily shows the bit line current control transistors63-1, 63-2 provided corresponding to the write bit lines WBL1, WBL2,respectively. Hereinafter, the bit line current control transistors arealso generally denoted with 63.

The bit line current control transistor 63 is electrically coupledbetween the corresponding write bit line WBL and a write data line /WDL,and is turned ON/OFF according to the voltage on the corresponding writerow selection line WRSL.

The data write circuit 51 b shown in FIG. 7 supplies the data writecurrent ±Iw to the write data lines WDL and /WDL. Thus, the data writecurrent ±Iw can be supplied to the write bit line WBL corresponding tothe selected memory cell row, according to the row selection result ofthe row decoder 20.

The read/write control circuit 60 further includes prechargingtransistors provided corresponding to the respective read bit lines RBL,and write bit line voltage control transistors provided corresponding tothe respective write bit lines WBL.

FIG. 35 exemplarily shows the precharging transistors 64-1, 64-2provided corresponding to the read bit lines RBL1, RBL2, and the writebit line voltage control transistors 65-1, 65-2 provided correspondingto the write bit lines WBL, WBL2, respectively. Hereinafter, theplurality of write bit line voltage control transistors are alsogenerally denoted with 65.

Each write bit line voltage control transistor 65 is turned ON in thedata read operation to couple the corresponding write bit line WBL tothe ground voltage Vss in order to ensure the current path of the sensecurrent Is. In the operation other than the data read operation, eachwrite bit line voltage control transistor 65 is turned OFF, so that eachwrite bit line WBL is disconnected from the ground voltage Vss. Sincethe operation of the precharging transistor 64 is the same as thatdescribed in connection with FIG. 2, description thereof will not berepeated.

With such a structure, in the data write operation, the data writecurrent ±Iw can be supplied to the write bit line WBL corresponding tothe selected memory cell row through the path formed from the write dataline WDL, write row selection gate WRSG, write bit line WBL, bit linecurrent control transistor 63 and write data line /WDL. Note that it ispossible to control the direction of the data write current ±Iw bysetting the voltage on the write data line WDL, /WDL in the same manneras that of the write data bus WDB, /WDB of the first embodiment.Accordingly, like the first embodiment, the structure of the peripheralcircuitry associated with the data write operation, i.e., the writecontrol circuit 50 w and 60 w can be simplified.

Thus, the data write and read operations as shown in FIG. 33 can beconducted even in the structure in which the read word lines RWL and thewrite word lines WWL extend perpendicularly to each other and the writebit line WBL and the read bit line RBL are shared between adjacentmemory cells.

With such a structure, the pitches of the write bit lines WBL and theread bit lines RBL in the memory array 10 can be widened. As a result,the memory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Such the widened pitch of the write bit lines WBL ensure an increasedline width of the write bit lines WBL. Accordingly, the followingeffects can further be obtained.

As described before, in the data write operation, the data write currentmust be supplied to both the write bit line WBL and the write word lineWWL.

As shown in FIG. 34, in the MTJ memory cell structure according to thefifth embodiment, the distance between the write bit line WBL and themagnetic tunnel junction MTJ in the vertical direction is larger thanthat between the write word line WWL and the magnetic tunnel junctionMTJ. Accordingly, in the data write operation, a larger current must besupplied to the write bit line WBL that is located farther from themagnetic tunnel junction MTJ.

However, the write bit line WBL is shared between adjacent memory cellcolumns. Therefore, the write bit line WBL can be arranged using thespace for two memory cell rows, whereby the line width of each write bitline WBL can be increased. Thus, a line width at least larger than thatof the write word line WWL, i.e., a larger cross-sectional area, of thewrite bit line WBL can be ensured As a result, the current density ofthe write word line WWL is suppressed.

The reliability of the MRAM device can thus be improved by sharing oneof the wirings requiring the data write current supply, i.e., the wiringthat is structurally located farther from the magnetic tunnel junctionMTJ, between adjacent memory cells.

For improved reliability, it is also effective to form a metal wilinghaving a large distance to the magnetic tunnel junction MTJ (the writebit line WBL in FIG. 34) from a highly electromigration-resistantmaterial. For example, in the case where the other metal wirings areformed from an aluminum alloy (Al alloy), the metal wirings that maypossibly be subjected to electromigration may be formed from copper(Cu).

First Modification of Fifth Embodiment

Referring to FIG. 37, in the memory array according to the firstmodification of the fifth embodiment, adjacent memory cells share thesame write word line WWL. For example, the memory cell group of thefirst and second memory cell columns shares a single write word lineWWL1. In the following memory cell columns as well, the write word linesWWL are arranged similarly.

In order to conduct the data write operation normally, a plurality ofmemory cells MC must not be present at the intersection of the samewrite word line WWL and the same write bit line WBL. Accordingly, thememory cells MC are arranged alternately.

Since the structure of the peripheral circuitry associated with the dataread and write operations through the read bit line RBL and write bitline WBL, as well as the memory cell operation in reading and writingthe data are the same as those of the fifth embodiment, detaileddescription thereof will not be repeated.

With such a structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Second Modification of Fifth Embodiment

Referring to FIG. 38, the memory array according to the secondmodification of the fifth embodiment is different from that of the firstmodification of the fifth embodiment in that adjacent memory cells inthe column direction also share the same read word line RWL. Forexample, the memory cell group of the first and second memory cell rowsshares the same read word line RWL1. In the following memory cell rowsas well, the read word lines RWL are arranged similarly.

In order to conduct the data read and write operations normally, aplurality of memory cells MC selected by a single read word line RWL orwrite word line WWL must not be simultaneously coupled to the same readbit line RBL or write bit line WBL. Accordingly, the read bit line RBLand the write bit line WBL are provided in every memory cell column andevery memory cell row, respectively, and the memory cells MC arearranged alternately.

Since the structure of the other portions and the memory cell operationin reading and writing the data are the same as those of the fifthembodiment, detailed description thereof will not be repeated.

With such a structure, the pitches of the read word lines RWL and writeword lines WWL in the memory array 10 can be widened. As a result, thememory cells MC can be more efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Third Modification of Fifth Embodiment

Referring to FIG. 39, for the memory cells having the structure of thefifth embodiment and arranged in rows and columns, the folded bit linestructure is realized in every set of adjacent two memory cell columns,using corresponding two read bit lines RBL. For example, a read bit linepair can be formed from the read bit lines RBL1 and RBL2 respectivelycorresponding to the first and second memory cell columns. In this case,the read bit line RBL2 is also referred to as read bit line /RBL1because it is complementary to the read bit line RBL1.

Hereinafter, one read bit line of each read bit line pair thatcorresponds to an odd memory cell column is also generally referred toas read bit line RBL, and the other read bit line that corresponds to aneven memory cell column is also generally referred to as read bit line/RBL.

A read column selection line is provided for every read bit line pair,i.e., every set of memory cell columns. Accordingly, two read columnselection gates RCSG corresponding to the same set are turned ON/OFF inresponse to the common read column selection line RCSL.

For example, the read column selection gates RCSG1 and RCSG2corresponding to the first and second memory cell columns operate inresponse to the common read column selection line RCSL1. The read columnselection gates RCSG1, RCSG3, . . . corresponding to the read bit linesRBL of the odd columns are each electrically coupled between thecorresponding read bit line RBL and the read data line RDL. The readcolumn selection gates RCSG2, RCSG4, . . . corresponding to the read bitlines /RBL of the even columns are each electrically coupled between thecorresponding read bit line /RBL and a read data line /RDL.

In response to the read column selection line RCSL activated accordingto the column selection result, corresponding two read column selectiongates RCSG are turned ON. As a result, the read bit lines RBL and /RBLof the read bit line pair corresponding to the selected memory cellcolumn are electrically coupled to the read data lines RDL and /RDL ofthe read data line pair, respectively.

Moreover, the same precharging transistors 64 as those described inconnection with FIG. 35 are provided corresponding to the respectivereal bit lines RBL and /RBL. As described before, the prechargingtransistors 64 are turned OFF in the data read operation.

As a result, the sense current Is is supplied from the data read circuit55 d to each of the read bit lines RBL and /RBL corresponding to theselected memory cell column through the read data lines RDL and /RDL.Since the structure of the data read circuit 55 d has been described inconnection with FIG. 15, detailed description thereof will not berepeated.

Accordingly, the data read operation is conducted using the same dummymemory cells DMC as those of the first embodiment each capable of beingselectively coupled to either the read bit line RBL or /RBL. Thus, thedata read margin can be ensured based on the so-called folded bit linestructure.

Similarly, the folded bit line structure is realized in every set ofadjacent two memory cell rows, using corresponding two write bit linesWBL. For example, a write bit line pair can be formed from the write bitlines WBL1 and WBL2 respectively corresponding to the first and secondmemory cell rows. In this case, the write bit line WBL2 is also referredto as write bit line /WBL1 because it is complementary to the write bitline WBL1.

In the following memory cell columns as well, the read bit lines RBL andthe write bit lines WBL are similarly arranged so as to form a read bitline pair and a write bit line pair in every set of memory cell columnsand rows, respectively.

One write bit line of each write bit line pair that corresponds to anodd memory cell row is also generally referred to as write bit line WBL,and the other write bit line that corresponds to an even memory cell rowis also generally referred to as write bit line /WBL. Thus, the datawrite operation can be conducted based on the so-called folded bit linestructure.

The write row selection line WRSL is provided for every write bit linepair, i.e., every set of memory cell rows. Accordingly, two write rowselection gates WRSG corresponding to the same set are turned ON/OFF inresponse to the common write row selection line WRSL.

For example, the write row selection gates WRSG1 and WRSG2 correspondingto the first and second memory cell rows operate in response to thecommon write row selection line WRSL1.

The write row selection gates WRSG1, WRSG3, . . . corresponding to thewrite bit lines WBL of the odd rows are each electrically coupledbetween the corresponding write bit line WBL and the write data lineWDL. The write row selection gates WRSG2, WRSG4, . . . corresponding tothe write bit lines /WBL of the even rows are each electrically coupledbetween the corresponding write bit line /WBL and the write data line/WDL.

In response to the write row selection line WRSL activated according tothe row selection result, corresponding two write row selection gatesWRSG are turned ON. As a result, the write bit lines WBL and /WBL of thewrite bit line pair corresponding to the selected memory cell row areelectrically coupled to the write data lines WDL and /WDL of the writedata line pair, respectively.

Moreover, the equalizing transistors 62 for connecting the write bitlines WBL and /WBL of the respective write bit line pair to each otherare provided instead of the bit line current control transistors 63shown in FIG. 35. The equalizing transistor 62 operates in response to,e.g., the control signal WE so as to short-circuit two write bit linesforming the same write bit line pair in the data write operation. Thesame write bit line voltage control transistors 65 as those described inconnection with FIG. 35 are provided corresponding to the respectivewrite bit lines WBL and /WBL.

The data write current ±Iw is supplied from the data write circuit 51 bto the write data lines WDL and /WDL of the write data line pair in thesame manner as that of the write data buses WDB and /WDB of the firstembodiment. Since the structure and operation of the data write circuit51 b have been described in connection with FIG. 7, detailed descriptionthereof will not be repeated.

As a result, the data write operation can be conducted in the write bitline pair corresponding to the row selection result, by using areciprocating current returned at the equalizing transistor 62.

With such a structure, in the data read operation, a selected read bitline pair is supplied with the sense current in the same manner as thatof the bit line pair of the first embodiment. Similarly, in the datawrite operation, a selected write bit line pair is supplied with thedata write current thorough the corresponding equalizing transistor 62in the same manner as that of the bit line pair of the first embodiment.

Therefore, in the case where the memory cells according to the fifthembodiment capable of reducing the chip area are arranged in rows andcolumns, the read and write operation margins can be ensured using thefolded bit line structure.

Fourth Modification of Fifth Embodiment

In the fourth modification of the fifth embodiment, the write bit lineWBL is shared between adjacent memory cells, in addition to the foldedbit line structure shown in the third modification of the fifthembodiment.

Referring to FIG. 40, in the memory array according to the fourthmodification of the fifth embodiment, adjacent memory cells in thecolumn direction share the same write bit line WBL.

In the read operation, the read word line RWL is activated. In each readbit line RBL, the memory cells are provided every other read word lineRWL. Moreover, the memory cells are arranged alternately between everyadjacent read bit lines RBL. Therefore, every set of adjacent two memorycell columns form a read bit line pair, so that the data read operationcan be conducted based on the folded bit line structure in the samemanner as that of the third modification of the fifth embodiment.

On the other hand, the data write operation cannot be conducted based onthe folded bit line structure because the write bit line WBL is shared.Accordingly, in the fourth modification of the fifth embodiment, theperipheral circuitry associated with selection of the write bit line WBLis arranged in the same manner as that shown in FIG. 35. Thus, as in thecase of the fifth embodiment, the data write operation can be conductedusing the data write circuit 51 b having a simple structure.

Although the data write operation cannot be conducted based on thefolded bit line structure, the pitch of the write bit lines WBL in thememory array 10 can be widened. As a result, further improvedintegration of the memory array 10 and thus further reduced chip area ofthe MRAM device can be achieved. Improved reliability of the MRAM devicecan also be achieved by increasing the electromigration resistance ofthe write bit lines WWL.

Note that, although FIG. 40 shows the structure in which the write bitline WBL out of the signal wirings associated with the data writeoperation is shared between adjacent memory cells, it is also possibleto share the write word line WWL instead of the write bit line WBL. Inthis case, however, the write bit line WBL cannot be shared, and must beprovided in every memory cell row. Which of the wirings should be sharedto widen the wiling pitch can be determined in view of the structuralconditions, design and the like, such as the distance from the magnetictunnel junction MTJ.

Fifth Modification of Fifth Embodiment

In the fifth modification of the fifth embodiment, the read word lineRWL is shared between adjacent memory cells, in addition to the foldedbit line structure of the third modification of the fifth embodiment.

Referring to FIG. 41, in the memory array according to the fifthmodification of the fifth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL.

The read/write control circuit 60 includes the equalizing transistors62, precharging transistors 64 and write bit line voltage controltransistors 65, which are arranged in the same manner as that of thethird modification of the fifth embodiment.

In the data write operation, the write word line WWL is activated. Ineach write bit line WBL, the memory cells are provided every other writeword line WWL. Moreover, the memory cell are arranged alternatelybetween every adjacent write bit lines WBL. Therefore, every set ofadjacent two memory cell rows can form a write bit line pair. As aresult, the data write operation can be conducted based on the foldedbit line structure in the same manner as that of the third modificationof the fifth embodiment, so that the same effects can be obtained.

On the other hand, in the data read operation, the read word line RWLshared by a plurality of memory cell rows is activated. Therefore, thedata read operation cannot be conducted based on the folded bit linestructure. Accordingly, in the fifth modification of the fifthembodiment, the peripheral circuitry associated with selection of theread bit line RBL is arranged in the same manner as that shown in FIG.35.

With such a structure, the read operation margin based on the folded bitline structure cannot be ensured, but the pitch of the read word linesRWL in the memory array 10 can be widened, and the data read operationcan be conducted normally. As a result, improved integration of thememory array 10 and thus reduced chip area of the MRAM device can beachieved.

Accordingly, by conducting the data write operation based on the foldedbit line structure using the memory cells of the fifth embodiment, thewrite operation margin can be ensured as well as a simplified structureof the peripheral circuitry and reduced data write noise can beachieved. Moreover, by sharing the read word line RWL, improvedintegration of the memory array 10 can also be achieved simultaneously.

Note that, although FIG. 41 shows the structure in which the read wordline RWL out of the signal wirings associated with the data readoperation is shared between adjacent memory cells, it is also possibleto share the read bit line RBL instead of the read word line RWL. Inthis case, however, the read word line RWL cannot be shared, and must beprovided in every memory cell row. Which of the wirings should be sharedto widen the wiring pitch can be determined as appropriate in view ofthe structural conditions, design and the like.

Sixth Embodiment

Referring to FIG. 42, the MTJ memory cell according to the sixthembodiment is different from that shown in FIG. 32 in connection betweenthe read bit line RBL and the write bit line WBL. More specifically, theread bit line RBL is not directly coupled to the magnetic tunneljunction MTJ, but coupled thereto in response to turning-ON of theaccess transistor ATR. Moreover, the write bit line WBL is coupled tothe magnetic tunnel junction MTJ so as to be included in the sensecurrent path in the data read operation.

Including the extending direction of each signal wiring, the structureis otherwise the same as that of FIG. 32. Therefore, detaileddescription thereof will not be repeated. Moreover, the voltage andcurrent waveforms of each wiling in the data read and write operationsare also the same as those of FIG. 33. Therefore, detailed descriptionthereof will not be repeated.

Accordingly, the write word line WWL is provided near the magnetictunnel junction MTJ so as to extend perpendicularly to the write bitline WBL. As a result, the read word line driver 30 r and the write wordline driver 30 w can be independently provided, whereby the same effectsas those of the fifth embodiment can be obtained.

Moreover, the write word line WWL can be independently provided withoutbeing coupled to other portions of the MTJ memory cell. Therefore, thewrite word line WWL can be arbitrarily arranged so as to improve themagnetic coupling with the magnetic tunnel junction MTJ.

Moreover, the read bit line RBL is coupled to the magnetic tunneljunction MTJ through the access transistor ATR. Therefore, the number ofmagnetic tunnel junctions MTJ coupled to the read bit lines RBL isreduced, and the capacitance of the read bit line RBL is reduced. As aresult, the data read speed can be increased.

Referring to FIG. 43, in the MTJ memory cell according to the sixthembodiment, the read bit line RBL is provided in the first metal wilinglayer Ml so as to be electrically coupled to the source/drain region 110of the access transistor ATR. The read word line RWL is provided in thesame layer as that of the gate 130 of the access transistor ATR. Thesource/drain region 120 of the access transistor ATR is coupled to themagnetic tunnel junction MTJ through the metal wirings provided in thefirst and second metal wiling layers M1 and M2, the barrier metal 140,and the metal film 150 provided in the contact hole.

The magnetic tunnel junction MTJ is provided between the second andthird metal wiring layers M2 and M3. The write bit line WBL is providedin the third metal wiring layer M3 so as to be electrically coupled tothe magnetic tunnel junction MTJ. The write word line WWL is provided inthe second metal wiling layer M2. At this time, the write word line WWLis provided so as to enable improved magnetic coupling with the magnetictunnel junction MTJ.

In the MTJ memory cell according to the sixth embodiment, the distancebetween the write bit line WBL and the magnetic tunnel junction MTJ canbe reduced as compared to that in the MTJ memory cell of the fifthembodiment shown in FIG. 34. Accordingly, the amount of data writecurrent flowing through the write bit line WBL can be reduced.

The write word line WWL is located farther from the magnetic tunneljunction MTJ than is the write bit line WBL. Therefore, in the MTJmemory cell of the sixth embodiment, a relatively large data writecurrent must be applied to the write word line WWL.

Referring to FIG. 44, in the memory array according to the sixthembodiment, the memory cells MC having the structure of FIG. 42 arearranged in rows and columns. The read word lines RWL and the write wordlines WWL extend in the row and column directions, respectively. Theread bit lines RBL and the write bit lines WBL extend in the column androw directions, respectively.

Adjacent memory cells in the row direction share the read bit line RBL,and adjacent memory cells in the column direction share the write bitline WBL.

For example, the memory cell group of the first and second memory cellcolumns shares the same read bit line RBL1, and the memory cell group ofthe third and fourth memory cell columns shares the same read bit lineRBL2. Moreover, the memory cell group of the second and third memorycell rows shares the write bit line WBL2. In the following memory cellrows and columns as well, the read bit lines RBL and the write bit linesWBL are arranged similarly.

If the data is to be read from or written to a plurality of memory cellsMC of the same read bit line RBL or write bit line WBL, data collisionoccurs. Accordingly, the memory cells MC are arranged alternately.

With such a structure, the pitches of the read bit lines RBL and thewrite bit lines WBL in the memory array 10 can be widened as in the caseof the fifth embodiment. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Since the structure of the peripheral circuitry for selectivelysupplying the data write current and the sense current to the read bitline RBL and the write bit line WBL is the same as that of FIG. 35,detailed description thereof will not be repeated.

First Modification of Sixth Embodiment

Referring to FIG. 45, in the memory array according to the firstmodification of the sixth embodiment, adjacent memory cells share thesame write word line WWL. For example, the memory cell group of thesecond and third memory cell columns shares a single write word lineWWL2. In the following memory cell columns as well, the write word linesWWL are arranged similarly.

In order to conduct the data write operation normally, a plurality ofmemory cells MC must not be present at the intersection of the samewrite word line WWL and the same write bit line WBL. Accordingly, thememory cells MC are arranged alternately.

Moreover, like the sixth embodiment, adjacent memory cells in the rowdirection share the read bit line RBL.

Since the structure of the peripheral circuitry associated with the dataread and write operations through the read bit line RBL and write bitline WBL, as well as the memory cell operation in reading and writingthe data are the same as those of the sixth embodiment, detaileddescription thereof will not be repeated.

As described before, in the MTJ memory cell of the sixth embodiment, arelatively large data write current must be applied to the write wordline WWL. Accordingly, the write word line WWL is shared betweenadjacent memory cells so as to ensure the line pitch thereof. As aresult, the line width, i.e., the cross-sectional area, of the writeword line WWL is assured, so that the current density thereof can besuppressed. As a result, improved reliability of the MRAM device can beachieved. As described before, for the improved operation reliability,it is also effective to select a material of these wirings in view ofelectromigration resistance.

Second Modification of Sixth Embodiment

Referring to FIG. 46, in the memory array according to the secondmodification of the sixth embodiment, adjacent memory cells in thecolumn direction also share the same read word line RWL. For example,the memory cell group of the second and third memory cell rows sharesthe same read word line RWL2. In the following memory cell rows as well,the read word lines RWL are arranged similarly.

In order to conduct the data read operation normally, a plurality ofmemory cells MC selected by the same read word line RWL must not besimultaneously coupled to the same read bit line RBL. Accordingly, theread bit line RBL is provided in every memory cell column, and thememory cells MC are arranged alternately.

With such a structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Third Modification of Sixth Embodiment

Referring to FIG. 47, for the memory cells having the structure of thesixth embodiment and arranged in rows and columns, the folded bit linestructure is realized in every set of adjacent two memory cell columns,using corresponding two read bit lines RBL. For example, a read bit linepair can be formed from the read bit lines RBL1 and RBL2 (/RBL1)respectively corresponding to the first-and second memory cell columns.

Similarly, the folded bit line structure is realized in every set ofadjacent two memory cell rows, using corresponding two write bit linesWBL. For example, a write bit line pair can be formed from the write bitlines WBL1 and WBL2 (/WBL1) respectively corresponding to the first andsecond memory cell rows.

The structure of the peripheral circuitry for conducting row selectionfrom the write bit lines WBL and /WBL of the write bit line pairs andsupplying the data write current ±Iw thereto, and for conducting columnselection from the read bit lines RBL and /RBL of the read bit linepairs and supplying the sense current Is thereto is the same as thatshown in FIG. 39. Therefore, detailed description thereof will not berepeated.

Accordingly, even when the memory cells according to the sixthembodiment are arranged in rows and columns, the read and writeoperation margins can be ensured using the folded bit line structure.

Fourth Modification of Sixth Embodiment

In the fourth modification of the sixth embodiment, the write bit lineWBL is shared between adjacent memory cells, in addition to the foldedbit line structure shown in the third modification of the sixthembodiment.

Referring to FIG. 48, in the memory array according to the fourthmodification of the sixth embodiment, adjacent memory cells in thecolumn direction share the same write bit line WBL.

In the read operation, the read word line RWL is activated. In each readbit line RBL, the memory cells are provided every other read word lineRWL. Moreover, the memory cells are arranged alternately between everyadjacent read bit lines RBL. Therefore, every set of adjacent two memorycell columns form a read bit line pair, so that the data read operationcan be conducted based on the folded bit line structure in the samemanner as that of the third modification of the sixth embodiment.

On the other hand, the data write operation cannot be conducted based onthe folded bit line structure because the write bit line WBL is shared.Accordingly, in the fourth modification of the sixth embodiment, theperipheral circuitry associated with selection of the write bit line WBLis arranged in the same manner as that shown in FIG. 44. Thus, as in thecase of the sixth embodiment, the data write operation can be conductedusing the data write circuit 51 b having a simple structure.

Although the data write operation cannot be conducted based on thefolded bit line structure, the pitch of the write bit lines WBL in thememory array 10 can be widened. As a result, further improvedintegration of the memory array 10 and thus further reduced chip area ofthe MRAM device can be achieved.

Note that, although FIG. 48 shows the structure in which the write bitline WBL out of the signal wirings associated with the data writeoperation is shared between adjacent memory cells, it is also possibleto share the write word line WWL instead of the write bit line WBL. Inthis case, however, the write bit line WBL cannot be shared, and must beprovided in every memory cell row. Which of the wirings should be sharedto widen the wiling pitch can be determined in view of the distance fromthe magnetic tunnel junction MTJ, and the like.

Fifth Modification of Sixth Embodiment

In the fifth modification of the sixth embodiment, the read word lineRWL is shared between adjacent memory cells, in addition to the foldedbit line structure of the third modification of the sixth embodiment.

Referring to FIG. 49, in the memory array according to the fifthmodification of the sixth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL.

The read/write control circuit 60 includes the equalizing transistors62, precharging transistors 64 and write bit line voltage controltransistors 65, which are arranged in the same manner as that of thethird modification of the sixth embodiment.

In the data write operation, the write word line WWL is activated. Ineach write bit line WBL, the memory cells are provided every other writeword line WWL. Moreover, the memory cells are arranged alternatelybetween every adjacent write bit lines WBL. Therefore, every set ofadjacent two memory cell rows can form a write bit line pair. As aresult, the data write operation can be conducted based on the foldedbit line structure in the same manner as that of the third modificationof the fifth embodiment, so that the same effects can be obtained.

On the other hand, in the data read operation, the read word line RWLshared by a plurality of memory cell rows is activated. Therefore, thedata read operation cannot be conducted based on the folded bit linestructure. Accordingly, in the fifth modification of the sixthembodiment, the peripheral circuitry associated with selection of theread bit line RBL is arranged in the same manner as that shown in FIG.44.

With such a structure, the read operation margin based on the folded bitline structure cannot be ensured, but the pitch of the read word linesRWL in the memory array 10 can be widened, and the data read operationcan be conducted normally. As a result, improved integration of thememory array 10 and thus reduced chip area of the MRAM device can beachieved.

Accordingly, by conducting the data write operation based on the foldedbit line structure using the memory cells of the sixth embodiment, thewrite operation margin can be ensured as well as a simplified structureof the peripheral circuitry and reduced data write noise can beachieved. Moreover, by sharing the read word line RWL, improvedintegration of the memory array 10 can also be achieved simultaneously.

Note that, although FIG. 49 shows the structure in which the read wordline RWL out of the signal wirings associated with the data readoperation is shared between adjacent memory cells, it is also possibleto share the read bit line RBL instead of the read word line RWL. Inthis case, however, the read word line RWL cannot be shared, and must beprovided in every memory cell row. Which of the wirings should be sharedto widen the wiling pitch can be determined as appropriate in view ofthe structural conditions, design and the like.

Seventh Embodiment

Referring to FIG. 50, in the MTJ memory cell according to the seventhembodiment, the read bit line RBL is coupled to the magnetic tunneljunction MTJ through the access transistor ATR. The magnetic tunneljunction MTJ is coupled between the write word line WWL and the accesstransistor ATR. The read word line RWL is coupled to the gate of theaccess transistor ATR. In the structure of FIG. 50 as well, the readword line RWL and the write word line WWL extend perpendicularly to eachother.

Referring to FIG. 51, the read bit line RBL is provided in the metalwiring layer Ml. The read word line RWL is formed in the same layer asthat of the gate 130 of the access transistor ATR. The read bit line RBLis coupled to the source/drain region 110 of the access transistor ATR.The source/drain region 120 is coupled to the magnetic tunnel junctionMTJ through the metal wirings provided in the first and second metalwiling layers M1 and M2, the barrier metal 140, and the metal film 150provided in the contact hole.

The write bit line WBL is provided in the second metal wiring layer M2near the magnetic tunnel junction MTJ. The write word line WWL isprovided in the third metal wiring layer M3 so as to be electricallycoupled to the magnetic tunnel junction MTJ.

With such a structure, the read bit line RBL is coupled to the magnetictunnel junction MTJ through the access transistor ATR. Accordingly, theread bit line RBL is electrically coupled only to the MTJ memory cell MCto be read, i.e., the MTJ memory cell MC of the memory cell rowcorresponding to the read word line RWL activated to the selected state(H level). Accordingly, the capacitance of the read bit line RBL can besuppressed, whereby a high-speed data read operation can be achieved.

Note that, in the MTJ memory cell of the seventh embodiment, the voltageand current waveforms of each wiling in the data read and writeoperations are the same as those of FIG. 33. Therefore, detaileddescription thereof will not be repeated.

In the MTJ memory cell according to the seventh embodiment as well, thedistance between the write bit line WBL and the magnetic tunnel junctionMTJ can be reduced as compared to that in the MTJ memory cell of thefifth embodiment shown in FIG. 34. Accordingly, the amount of data writecurrent flowing through the write bit line WBL can be reduced.

The write bit line WBL is located farther from the magnetic tunneljunction MTJ than is the write word line WWL. Therefore, in the MTJmemory cell of the seventh embodiment, a relatively large data writecurrent must be applied to the write bit line WBL.

Referring to FIG. 52, in the memory array according to the seventhembodiment, the memory cells MC shown in FIG. 50 are arranged in rowsand columns. The read word lines RWL and the write word lines WWL extendin the row and column directions, respectively. The read bit lines RBLand the write bit lines WBL extend in the column and row directions,respectively.

Adjacent memory cells in the row direction share the read bit line RBL,and adjacent memory cells in the column direction share the write bitline WBL.

For example, the memory cell group of the first and second memory cellcolumns shares the same read bit line RBL1, and the memory cell group ofthe third and fourth memory cell columns shares the same read bit lineRBL2. Moreover, the memory cell group of the second and third memorycell rows shares the write bit line WBL2. In the following memory cellrows and columns as well, the read bit lines RBL and the write bit linesWBL are arranged similarly.

If the data is to be read from or written to a plurality of memory cellsMC of the same read bit line RBL or write bit line WBL, data collisionoccurs. Accordingly, the memory cells MC are arranged alternately.

With such a structure, the pitches of the read bit lines RBL and thewrite bit lines WBL in the memory array 10 can be widened. As a result,the memory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Since the structure of the peripheral circuitry for selectivelysupplying the data write current and the sense current to the read bitline RBL and the write bit line WBL is the same as that of FIG. 35,detailed description thereof will not be repeated.

As described before, in the MTJ memory cell of the seventh embodiment, arelatively large data write current must be applied to the write bitline WBL. Accordingly, the write bit line WBL is shared between adjacentmemory cells so as to ensure the line pitch thereof. As a result, theline width, i.e., the cross-sectional area, of the write bit line WBL isassured, so that the current density thereof can be suppressed. As aresult, improved reliability of the MRAM device can be achieved. Asdescribed before, for the improved operation reliability, it is alsoeffective to select a material of these wirings in view ofelectromigration resistance.

First Modification of Seventh Embodiment

Referring to FIG. 53, in the memory array according to the firstmodification of the seventh embodiment, adjacent memory cells share thesame write word line WWL. For example, the memory cell group of thesecond and third memory cell columns shares a single write word lineWWL2. In the following memory cell columns as well, the write word linesWWL are arranged similarly.

In order to conduct the data write operation normally, a plurality ofmemory cells MC must not be present at the intersection of the samewrite word line WWL and the same write bit line WBL. Accordingly, thememory cells MC are arranged alternately.

Moreover, like the seventh embodiment, adjacent memory cells in the rowdirection share the read bit line RBL.

Since the structure of the peripheral circuitry associated with the dataread and write operations through the read bit line RBL and write bitline WBL, as well as the memory cell operation in reading and writingthe data are the same as those of the seventh embodiment, detaileddescription thereof will not be repeated.

With such a structure, the pitches of the read bit lines RBL and thewrite word lines WWL in the memory array 10 can be widened As a result,the memory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Second Modification of Seventh Embodiment

Referring to FIG. 54, in the memory array according to the secondmodification of the seventh embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL. For example, thememory cell group of the second and third memory cell rows shares thesame read word line RWL2. In the following memory cell rows as well, theread word lines RWL are arranged similarly.

Moreover, adjacent memory cells in the row direction share the samewrite word line WWL. For example, the memory cell group of the secondand third memory cell columns shares the same write word line WWL2. Inthe following memory cell columns as well, the write word lines WWL arearranged similarly.

In order to conduct the data read and write operations normally, aplurality of memory cells MC selected by the same read word line RWL orwrite word line WWL must not be simultaneously coupled to the same readbit line RBL or write bit line WBL. Accordingly, the read bit line RBLand the write bit line WBL are provided in every memory cell column andevery memory cell row, respectively, and the memory cells MC arearranged alternately.

Since the structure is otherwise the same as that of the seventhembodiment, detailed description thereof will not be repeated.

With such a structure, the pitches of the write word lines WWL and readword lines RWL in the memory array 10 can be widened. As a result, thememory cells MC can be more efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Third Modification of Seventh Embodiment

Referring to FIG. 55, for the memory cells having the structure of theseventh embodiment and arranged in rows and columns, the folded bit linestructure is realized in every set of adjacent two memory cell columns,using corresponding two read bit lines RBL. For example, a read bit linepair can be formed from the read bit lines RBL1 and RBL2 (/RBL1)respectively corresponding to the first and second memory cell columns.

Similarly, the folded bit line structure is realized in every set ofadjacent two memory cell rows, using corresponding two write bit linesWBL. For example, a write bit line pair can be formed from the write bitlines WBL1 and WBL2 (/WBL1) respectively corresponding to the first andsecond memory cell rows.

The structure of the peripheral circuitry for conducting row selectionfrom the write bit lines WBL and /WBL of the write bit line pairs andsupplying the data write current ±Iw thereto, and for conducting columnselection from the read bit lines RBL and /RBL of the read bit linepairs and supplying the sense current Is thereto is the same as thatshown in FIG. 39. Therefore, detailed description thereof will not berepeated.

Accordingly, even when the memory cells according to the seventhembodiment are arranged in rows and columns, the read and writeoperation margins can be ensured using the folded bit line structure.

Fourth Modification of Seventh Embodiment

In the fourth modification of the seventh embodiment, the write wordline WWL is shared between adjacent memory cells, in addition to thefolded bit line structure shown in the third modification of the seventhembodiment.

Referring to FIG. 56, in the memory array according to the fourthmodification of the seventh embodiment, adjacent memory cells in the rowdirection share the same write word line WWL.

In the read operation, the read word line RWL is activated. In each readbit line RBL, the memory cells are provided every other read word lineRWL. Moreover, the memory cells are arranged alternately between everyadjacent read bit lines RBL. Therefore, every set of adjacent two memorycell columns form a read bit line pair, so that the data read operationcan be conducted based on the folded bit line structure in the samemanner as that of the third modification of the seventh embodiment.

On the other hand, the data write operation cannot be conducted based onthe folded bit line structure because the write word line WWL is shared.Accordingly, in the fourth modification of the seventh embodiment, theperipheral circuitry associated with selection of the write bit line WBLis arranged in the same manner as that shown in FIG. 52. Thus, as in thecase of the seventh embodiment, the data write operation can beconducted using the data write circuit 51 b having a simple structure.

Although the data write operation cannot be conducted based on thefolded bit line structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, further improvedintegration of the memory array 10 and thus further reduced chip area ofthe MRAM device can be achieved.

Note that, although FIG. 56 shows the structure in which the write wordline WWL out of the signal wirings associated with the data writeoperation is shared between adjacent memory cells, it is also possibleto share the write bit line WBL instead of the write word line WWL. Inthis case, however, the write word line WWL cannot be shared, and mustbe provided in every memory cell column. Which of the wirings should beshared to widen the wiring pitch can be determined in view of thedistance from the magnetic tunnel junction MTJ, and the like.

Fifth Modification of Seventh Embodiment

In the fifth modification of the seventh embodiment, the read word lineRWL is shared between adjacent memory cells, in addition to the foldedbit line structure of the third modification of the seventh embodiment.

Referring to FIG. 57, in the memory array according to the fifthmodification of the seventh embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL.

The read/write control circuit 60 includes the equalizing transistors62, precharging transistors 64 and write bit line voltage controltransistors 65, which are arranged in the same manner as that of thethird modification of the seventh embodiment.

In the data write operation, the write word line WWL is activated. Ineach write bit line WBL, the memory cells are provided every other writeword line WWL. Moreover, the memory cells are arranged alternatelybetween every adjacent write bit lines WBL. Therefore, every set ofadjacent two memory cell rows can form a write bit line pair. As aresult, the data write operation can be conducted based on the foldedbit line structure in the same manner as that of the third modificationof the fifth embodiment, so that the same effects can be obtained.

On the other hand, in the data read operation, the read word line RWLshared by a plurality of memory cell rows is activated. Therefore, thedata read operation cannot be conducted based on the folded bit linestructure. Accordingly, in the fifth modification of the seventhembodiment, the peripheral circuitry associated with selection of theread bit line RBL is arranged in the same manner as that shown in FIG.52.

With such a structure, the read operation margin based on the folded bitline structure cannot be ensured, but the pitch of the read word linesRWL in the memory array 10 can be widened, and the data read operationcan be conducted normally. As a result, improved integration of thememory array 10 and thus reduced chip area of the MRAM device can beachieved.

Accordingly, by conducting the data write operation based on the foldedbit line structure using the memory cells of the seventh embodiment, thewrite operation margin can be ensured as well as a simplified structureof the peripheral circuitry and reduced data write noise can beachieved. Moreover, by sharing the read word line RWL, improvedintegration of the memory array 10 can also be achieved simultaneously.

Note that, although FIG. 57 shows the structure in which the read wordline RWL out of the signal wirings associated with the data readoperation is shared between adjacent memory cells, it is also possibleto share the read bit line RBL instead of the read word line RWL. Inthis case, however, the read word line RWL cannot be shared, and must beprovided in every memory cell row. Which of the wirings should be sharedto widen the wiring pitch can be determined as appropriate in view ofthe structural conditions, design and the like.

Eighth Embodiment

Referring to FIG. 58, the MTJ memory cell according to the eighthmodification is different from that of the seventh embodiment shown inFIG. 50 in that the read bit line RBL and the write word line WWL areswitched in position. Since the arrangement of the lines is otherwisethe same as that of FIG. 50, description thereof will not be repeated.Such a structure also allows the read word line RWL and the write wordline WWL to extend perpendicularly to each other.

Referring to FIG. 59, the structure of the MTJ memory cell according tothe eighth embodiment is different from that of the seventh embodimentshown in FIG. 51 in that the write word line WWL and the read bit lineRBL are switched in position. More specifically, the write word line WWLis provided in the first metal wiling layer M1 so as to be coupled tothe source/drain region 110 of the access transistor ATR. The read bitline RBL is provided in the third metal wiling layer M3 so as to beelectrically coupled to the magnetic tunnel junction MTJ.

In the eighth embodiment, the read bit line RBL is directly coupled tothe magnetic tunnel junction MTJ. Therefore, such an increased readoperation speed as in the seventh embodiment cannot be achieved.However, in the structure of the eighth embodiment as well, the readword line driver 30 r and the write word line driver 30 w can beindependently provided, whereby the same effects as those of the seventhembodiment can be obtained.

Note that, in the MTJ memory cell of the eighth embodiment, the voltageand current waveforms of each wiling in the data read and writeoperations are the same as those of FIG. 33. Therefore, detaileddescription thereof will not be repeated.

In the MTJ memory cell according to the eighth embodiment, the writeword line WWL is located farther from the magnetic tunnel junction MTJthan is the write bit line WBL. Therefore, a relatively large data writecurrent must be applied to the write word line WWL.

Referring to FIG. 60, in the memory array according to the eighthembodiment, the memory cells MC having the structure shown in FIG. 58are arranged in rows and columns. The read word lines RWL and the writeword lines WWL extend in the row and column directions, respectively.The read bit lines RBL and the write bit lines WBL extend in the columnand row directions, respectively.

Adjacent memory cells in the row direction share the same write wordline WWL.

For example, the memory cell group of the first and second memory cellcolumns shares the same write word line WWL1, and the memory cell groupof the third and fourth memory cell columns shares the same write wordline WWL2. In the following memory cell columns as well, the write wordlines WWL are arranged similarly.

If the data is to be written to a plurality of memory cells MC of thesame write bit line WBL, data collision occurs. Accordingly, the memorycells MC are arranged alternately.

With such a structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Since the structure of the peripheral circuitry for selectivelysupplying the data write current and the sense current to the read bitline RBL and the write bit line WBL is the same as that of FIG. 35,detailed description thereof will not be repeated.

As described before, in the MTJ memory cell of the eighth embodiment, arelatively large data write current must be applied to the write wordline WWL. Accordingly, the write word line WWL is shared betweenadjacent memory cells so as to ensure the line pitch thereof. As aresult, the line width, i.e., the cross-sectional area, of the writeword line WWL is assured, so that the current density thereof can besuppressed. Thus, improved reliability of the MRAM device can beachieved. As described before, for the improved operation reliability,it is also effective to select a material of these wirings in view ofelectromigration resistance.

First Modification of Eighth Embodiment

Referring to FIG. 61, in the memory array according to the firstmodification of the eighth embodiment, adjacent memory cells share thesame read bit line RBL. For example, the memory cell group of the secondand third memory cell columns shares the same read bit line RBL2. In thefollowing memory cell columns as well, the read bit lines RBL arearranged similarly.

In order to conduct the data read operation normally, a plurality ofmemory cells MC must not be present at the intersection of the same readword line RWL and the same read bit-line RBL. Accordingly, the memorycells MC are arranged alternately.

Moreover, adjacent memory cells share the same write bit line WBL. Forexample the memory cell group of the first and second memory cell rowsshares the same write bit line WBL1. In the following memory cell rowsas well, the write bit lines WBL are arranged similarly.

In order to conduct the data write operation normally, a plurality ofmemory cells MC must not be present at the intersection of the samewrite word line WWL and the same write bit line WBL.

Since the structure of the peripheral circuitry associated with the dataread and write operations through the read bit line RBL and write bitline WBL, as well as the memory cell operation in reading and writingthe data are the same as those of the eighth embodiment, detaileddescription thereof will not be repeated.

With such a structure, the pitches of the read bit lines RBL and thewrite bit lines WBL in the memory array 10 can be widened. As a result,the memory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Second Modification of Eighth Embodiment

Referring to FIG. 62, in the memory array according to the secondmodification of the eighth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL. For example, thememory cell group of the second and third memory cell rows shares thesame read word line RWL2. In the following memory cell rows as well, theread word lines RWL are arranged similarly.

Moreover, adjacent memory cells in the column direction share the samewrite bit line WBL. For example, the memory cell group of the first andsecond memory cell rows shares the same write bit line WBL1. In thefollowing memory cell rows as well, the write bit lines WBL are arrangedsimilarly.

In order to conduct the data read operation normally, a plurality ofmemory cells MC selected by the same read word line RWL must not besimultaneously coupled to the same read bit line RBL. Accordingly, theread bit line RBL is provided in every memory cell column, and thememory cells MC are arranged alternately.

Since the structure is otherwise the same as that of the eighthembodiment, detailed description thereof will not be repeated.

With such a structure, the pitch of the read word lines RWL in thememory array 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Third Modification of Eighth Embodiment

Referring to FIG. 63, for the memory cells having the structure of theeighth embodiment and arranged in rows and columns, the folded bit linestructure is realized in every set of adjacent two memory cell columns,using corresponding two read bit lines RBL. For example, a read bit linepair can be formed from the read bit lines RBL1 and RBL2 (/RBL1)respectively corresponding to the first and second memory cell columns.

Similarly, the folded bit line structure is realized in every set ofadjacent two memory cell rows, using corresponding two write bit linesWBL. For example, a write bit line pair can be formed from the write bitlines WBL1 and WBL2 (/WBL1) respectively corresponding to the first andsecond memory cell rows.

The structure of the peripheral circuitry for conducting row selectionfrom the write bit lines WBL and /WBL of the write bit line pairs andsupplying the data write current ±Iw thereto, and for conducting columnselection from the read bit lines RBL and /RBL of the read bit linepairs and supplying the sense current Is thereto is the same as thatshown in FIG. 39. Therefore, detailed description thereof will not berepeated.

Accordingly, even when the memory cells according to the eighthembodiment are arranged in rows and columns, the data read and writeoperation margins can be ensured using the folded bit line structure.

Fourth Modification of Eighth Embodiment

In the fourth modification of the eighth embodiment, the write word lineWWL is shared between adjacent memory cells, in addition to the foldedbit line structure shown in the third modification of the eighthembodiment.

Referring to FIG. 64, in the memory array according to the fourthmodification of the eighth embodiment, adjacent memory cells in the rowdirection share the same write word line WWL.

In the read operation, the read word line RWL is activated. In each readbit line RBL, the memory cells are provided every other read word lineRWL. Moreover, the memory cells are arranged alternately between everyadjacent read bit lines RBL. Therefore, every set of adjacent two memorycell columns form a read bit line pair, so that the data read operationcan be conducted based on the folded bit line structure in the samemanner as that of the third modification of the eighth embodiment.

On the other hand, the data write operation cannot be conducted based onthe folded bit line structure because the write word line WWL is shared.Accordingly, in the fourth modification of the eighth embodiment, theperipheral circuitry associated with selection of the write bit line WBLis arranged in the same manner as that shown in FIG. 60. Thus, as in thecase of the eighth embodiment, the data write operation can be conductedusing the data write circuit 51 b having a simple structure.

Although the data write operation cannot be conducted based on thefolded bit line structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, further improvedintegration of the memory array 10 and thus further reduced chip area ofthe MRAM device can be achieved.

Note that, although FIG. 64 shows the structure in which the write wordline WWL out of the signal wirings associated with the data writeoperation is shared between adjacent memory cells, it is also possibleto share the write bit line WBL instead of the write word line WWL. Inthis case, however, the write word line WWL cannot be shared, and mustbe provided in every memory cell column. Which of the wirings should beshared to widen the wiring pitch can be determined in view of thedistance from the magnetic tunnel junction MTJ, and the like.

Fifth Modification of Eighth Embodiment

In the fifth modification of the eighth embodiment, the read word lineRWL is shared between adjacent memory cells, in addition to the foldedbit line structure of the third modification of the eighth embodiment.

Referring to FIG. 65, in the memory array according to the fifthmodification of the eighth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL.

The read/write control circuit 60 includes the equalizing transistors62, precharging transistors 64 and write bit line voltage controltransistors 65, which are arranged in the same manner as that of thethird modification of the eighth embodiment.

In the data write operation, the write word line WWL is activated. Ineach write bit line WBL, the memory cells are provided every other writeword line WWL. Moreover, the memory cells are arranged alternatelybetween every adjacent write bit lines WBL. Therefore, every set ofadjacent two memory cell rows can form a write bit line pair. As aresult, the data write operation can be conducted based on the foldedbit line structure in the same manner as that of the third modificationof the eighth embodiment, so that the same effects can be obtained.

On the other hand, in the data read operation, the read word line RWLshared by a plurality of memory cell rows is activated. Therefore, thedata read operation cannot be conducted based on the folded bit linestructure. Accordingly, in the fifth modification of the eighthembodiment, the peripheral circuitry associated with selection of theread bit line RBL is arranged in the same manner as that shown in FIG.60.

With such a structure, the read operation margin based on the folded bitline structure cannot be ensured, but the pitch of the read word linesRWL in the memory array 10 can be widened, and the data read operationcan be conducted normally. As a result, improved integration of thememory array 10 and thus reduced chip area of the MRAM device can beachieved.

Accordingly, by conducting the data write operation based on the foldedbit line structure using the memory cells of the eighth embodiment, thewrite operation margin can be ensured as well as a simplified structureof the peripheral circuitry and reduced data write noise can beachieved. Moreover, by sharing the read word line RWL, improvedintegration of the memory array 10 can also be achieved simultaneously.

Note that, although FIG. 65 shows the structure in which the read wordline RWL out of the signal wirings associated with the data readoperation is shared between adjacent memory cells, it is also possibleto share the read bit line RBL instead of the read word line RWL. Inthis case, however, the read word line RWL cannot be shared, and must beprovided in every memory cell row. Which of the wirings should be sharedto widen the wiling pitch can be determined as appropriate in view ofthe structural conditions, design and the like.

Ninth Embodiment

Referring to FIG. 66, in the MTJ memory cell according to the ninthembodiment, the access transistor ATR is electrically coupled betweenthe magnetic tunnel junction MTJ and the write bit line WBL. Themagnetic tunnel junction MTJ is coupled between the access transistorATR and a common line CML. The access transistor ATR has its gatecoupled to the read word line RWL. In the structure of FIG. 66 as well,the common line CML serving as a write word line WWL and the read wordline RWL extend perpendicularly to each other. Therefore, the respectivedrive circuits for the common line CML and the read word line RWL can beseparately provided, whereby the freedom of layout design can beimproved.

FIG. 67 is a timing chart illustrating the data write and readoperations to and from the MTJ memory cell according to the ninthembodiment.

Referring to FIG. 67, in the data write operation, the data writecurrent ±Iw is supplied to the write bit line WBL. Moreover, in responseto turning-ON of a current control transistor described below, the datawrite current Ip flows through the common line CML corresponding to theselected column, according to the column selection result. Thus, thevoltage and current on the common line CML in the data write operationare set in the same manner as those of the write word line WWL shown inFIG. 33.

As a result, the magnetic field corresponding to the level of the writedata DIN can be written to the magnetic tunnel junction MTJ. Moreover,as shown in FIG. 33, the read bit lines RBL are not required during thedata write operation. Therefore, the respective functions of the readbit line RBL and the write word line WWL can be integrated into thecommon line CML.

In the operation other than the data write operation, the aforementionedcurrent control transistors are turned OFF. The common lines CML areprecharged to the ground voltage Vss before the data read operation.

In the data read operation, the voltage level on the write bit lines WBLis set to the ground voltage level Vss. Moreover, the sense current Isfor the data read operation is supplied to the common line CML.Accordingly, in the data read operation, the read word line RWL isactivated to the selected state (H level) so as to turn ON the accesstransistor ATR. Thus, the sense current Is can be supplied through thepath formed by the common line CML, magnetic tunnel junction MTJ, accesstransistor ATR, and write bit line WBL.

When the current path of the sense current Is is formed in the MTJmemory cell, a voltage change (rise) corresponding to the storage datais produced on the common line CML.

It is now assumed in FIG. 67 that the fixed magnetic layer FL and thefree magnetic layer VL have the same magnetic field direction when thestorage data level is “1”. In this case, the common line CML has a smallvoltage change ΔV1 when the storage data is “1”, and has a voltagechange ΔV2 larger than ΔV1 when the storage data is “0”. The storagedata in the MTJ memory cell can be read by sensing the differencebetween the voltage changes ΔV1 and ΔV2 on the common line CML.

Moreover, as shown in FIG. 33, the write word lines WWL are not requiredduring the data read operation. Therefore, the write word lines WWL andthe read bit lines RBL can be integrated into the common lines CML.

Thus, the same data write and read operations can be conducted even withthe MTJ memory cell that uses the common line CML integrating therespective functions of the write word line WWL and the read bit lineRBL so as to reduce the number of wirings.

The precharge voltage of the common lines CML functioning as the readbit lines RBL in the data read operation is set to the same voltagelevel as that of the common lines CML in the data write operation, i.e.,the ground voltage Vss. As a result, a precharge operation inpreparation for the read data operation can be performed moreefficiently, whereby the data read operation speed can be increased.

Referring to FIG. 68, in the MTJ memory cell according to the ninthembodiment, the write bit line WBL is provided in the first metal wilinglayer M1, and the read word line RWL is provided in the same layer asthat of the gate 130 of the access transistor ATR. The write bit lineWBL is electrically coupled to the source/drain region 110 of the accesstransistor ATR. The other source/drain region 120 is coupled to themagnetic tunnel junction MTJ through the metal wiling provided in thefirst metal wiring layer M1, the barrier metal 140, and the metal film150 provided in the contact hole.

The common line CML is provided in the second metal wiring layer M2 soas to be electrically coupled to the magnetic tunnel junction MTJ. Sincethe common line CML has both functions of the read bit line RBL and thewrite word line WWL, reduction in the number of wirings as well as thenumber of metal wiring layers, and thus reduction in the manufacturingcost can be achieved in addition to the effects obtained by the MTJmemory cell according to the sixth embodiment.

In the MTJ memory cell according to the ninth embodiment, the write bitline WBL is located farther from the magnetic tunnel junction MTJ thanis the common line CML functioning as write word line WWL. Therefore, inthe MTJ memory cell of the ninth embodiment, a relatively large datawrite current must be applied to the write bit line WBL.

Referring to FIG. 69, in the memory array according to the ninthembodiment, the memory cells MC shown in FIG. 66 are arranged in rowsand columns. The read word lines RWL and the write bit lines WBL extendin the row direction. The common lines CML extend in the columndirection. Like the read word lines RWL and the like, the common linesCML are also generally denoted with CML, and a specific common line isdenoted with CML1, and the like.

Adjacent memory cells in the row direction share the same common lineCML.

For example, the memory cell group of the first and second memory cellcolumns shares the same common line CML1, and the memory cell group ofthe third and fourth memory cell columns shares the same common lineCML2. In the following memory cell columns as well, the common lines CMLare arranged similarly.

If the data is to be read from or written to a plurality of memory cellsMC of the same common line CML, data collision occurs. Accordingly, thememory cells MC are arranged alternately.

With such a structure, the pitch of the common lines CML in the memoryarray 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

The peripheral circuitry for selectively supplying the sense current,which is provided for the read bit lines RBL in FIG. 35, is provided forthe common lines CML.

Current control transistors are provided corresponding to the respectivecommon lines CML. FIG. 69 exemplarily shows the current controltransistors 41-1 and 41-2 respectively corresponding to the common linesCML1 and CML2 Hereinafter, the current control transistors are generallydenoted with 41.

The current control transistor 41 is provided between the correspondingcommon line CML and the ground voltage Vss. In the data write operationin which the common line CML functions as a write word line WWL, thecurrent control transistor 41 is turned ON in response to activation ofthe control signal WE, so that the write word line driver 30 w cansupply the data write current Ip to the common line CML activated to theselected state (power supply voltage Vcc).

As described in connection with FIG. 67, the common lines CML areprecharged to the ground voltage Vss before the data read operation.Therefore, the precharging transistors 44 can be omitted by making thecurrent control transistors 41 operate also in response to the bit lineprecharging signal BLPR.

Since the structure of the peripheral circuitry for selectivelysupplying the data write current to the write bit line WBL is the sameas that of FIG. 35, detailed description thereof will not be repeated.

First Modification of Ninth Embodiment

Referring to FIG. 70, in the memory array according to the firstmodification of the ninth embodiment, adjacent memory cells share thesame write bit line WBL. For example, the memory cell group of thesecond and third memory cell rows shares the same write bit line WBL2.In the following memory cell columns as well, the write bit lines WBLare arranged similarly.

In order to conduct the data write operation normally, a plurality ofmemory cells MC must not be present at the intersection of the samecommon line CML and the same write bit line WBL. Accordingly, the commonline CML is provided in every column, and the memory cells MC arearranged alternately.

Since the structure of the peripheral circuitry associated with the dataread and write operations through the common line CML and write bit lineWBL, as well as the memory cell operation in reading and writing thedata are the same as those of the ninth embodiment, detailed descriptionthereof will not be repeated.

With such a structure, the pitch of the write bit lines WBL in thememory array 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

As described before, in the MTJ memory cell of the ninth embodiment, arelatively large data write current must be applied to the write bitline WBL. Accordingly, the write bit line WBL is shared between adjacentmemory cells so as to ensure the line pitch thereof. As a result, theline width, i.e., the cross-sectional area, of the write bit line WBL isassured, so that the current density thereof can be suppressed. As aresult, improved reliability of the MRAM device can be achieved. Asdescribed before, for the improved operation reliability, it is alsoeffective to select a material of these wirings in view ofelectromigration resistance.

Second Modification of Ninth Embodiment

Referring to FIG. 71, in the memory array according to the secondmodification of the ninth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL. For example, thememory cell group of the first and second memory cell rows shares thesame read word line RWL1. In the following memory cell rows as well, theread word lines RWL are arranged similarly.

Moreover, adjacent memory cells in the column direction share the samewrite bit line WBL. For example, the memory cell group of the second andthird memory cell rows shares the same write bit line WBL2. In thefollowing memory cell rows as well, the write bit lines WBL are arrangedsimilarly.

In order to conduct the data read operation normally, a plurality ofmemory cells MC selected by the same read word line RWL must not besimultaneously coupled to the same common line CML. Accordingly, thecommon line CML is provided in every memory cell column, and the memorycells MC are arranged alternately.

Since the structure is otherwise the same as that of the ninthembodiment, detailed description thereof will not be repeated.

With such a structure, the pitches of the read word lines RWL and writebit lines WBL in the memory array 10 can be widened. As a result, thememory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Third Modification of Ninth Embodiment

Referring to FIG. 72, for the memory cells having the structure of theninth embodiment and arranged in rows and columns, the folded bit linestructure is realized in every set of adjacent two memory cell columns,using corresponding two common lines CML. For example, a data line paircorresponding to a read bit line pair can be formed from the commonlines CML1 and CML2 (/CML1) respectively corresponding to the first andsecond memory cell columns.

Similarly, the folded bit line structure is realized in every set ofadjacent two memory cell rows, using corresponding two write bit linesWBL. For example, a write bit line pair can be formed from the write bitlines WBL1 and WBL2 (/WBL1) respectively corresponding to the first andsecond memory cell rows.

The structure of the peripheral circuitry for conducting row selectionfrom the write bit lines WBL and /WBL of the write bit line pairs andsupplying the data write current ±Iw thereto is the same as that shownin FIG. 39. Therefore, detailed description thereof will not berepeated.

Moreover, provided that one of the common lines forming each data linepair in the data read operation is generally denoted with CML and theother is generally denoted with /CML, the peripheral circuitry forconducting column selection from the read bit lines RBL and /RBL in thestructure of FIG. 39 and supplying the sense current Is thereto isprovided corresponding to the common lines CML and /CML.

Accordingly, even when the memory cells according to the ninthembodiment are arranged in rows and columns, the data read and writeoperation margins can be ensured using the folded bit line structure.

Fourth Modification of Ninth Embodiment

In the fourth modification of the ninth embodiment, the write bit lineWBL is shared between adjacent memory cells, in addition to the foldedbit line structure shown in the third modification of the ninthembodiment.

Referring to FIG. 73, in the memory array according to the fourthmodification of the ninth embodiment, adjacent memory cells in thecolumn direction share the same write bit line WBL.

In the read operation, the read word line RWL is activated. In eachcommon line CML functioning as a read bit line RBL, the memory cells areprovided every other read word line RWL. Moreover, the memory cells arearranged alternately between every adjacent common lines CML. Therefore,every set of adjacent two memory cell columns form a data line pair, sothat the data read operation can be conducted based on the folded bitline structure in the same manner as that of the third modification ofthe ninth embodiment.

On the other hand, the data write operation cannot be conducted based onthe folded bit line structure because the write bit line WBL is shared.Accordingly, in the fourth modification of the ninth embodiment, theperipheral circuitry associated with selection of the write bit line WBLis arranged in the same manner as that shown in FIG. 69. Thus, as in theninth embodiment, the data write operation can be conducted using thedata write circuit 51 b having a simple structure.

Although the data write operation cannot be conducted based on thefolded bit line structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, further improvedintegration of the memory array 10 and thus further reduced chip area ofthe MRAM device can be achieved.

Fifth Modification of Ninth Embodiment

In the fifth modification of the ninth embodiment, the read word lineRWL is shared between adjacent memory cells, in addition to the foldedbit line structure of the third modification of the ninth embodiment.

Referring to FIG. 74, in the memory array according to the fifthmodification of the ninth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL.

The read/write control circuit 60 includes the equalizing transistors 62and the write bit line voltage control transistors 65, which arearranged in the same manner as that of the third modification of theninth embodiment.

In each write bit line WBL, the memory cells are provided every othercommon line CML. Moreover, the memory cells are arranged alternatelybetween every adjacent write bit lines WBL. Therefore, in the data writeoperation, every set of adjacent two memory cell rows can form a writebit line pair. As a result, the data write operation can be conductedbased on the folded bit line structure in the same manner as that of thethird modification of the ninth embodiment, so that the same effects canbe obtained.

On the other hand, in the data read operation, the read word line RWLshared by a plurality of memory cell rows is activated. Therefore, thedata read operation cannot be conducted based on the folded bit linestructure. Accordingly, in the fifth modification of the ninthembodiment, the peripheral circuitry associated with selection of thecommon line CML functioning as a read bit line RBL is arranged in thesame manner as that shown in FIG. 69.

With such a structure, the read operation margin based on the folded bitline structure cannot be ensured, but the pitch of the read word linesRWL in the memory array 10 can be widened, and the data read operationcan be conducted normally. As a result, improved integration of thememory array 10 and thus reduced chip area of the MRAM device can beachieved.

Accordingly, by conducting the data write operation based on the foldedbit line structure using the memory cells of the ninth embodiment, thewrite operation margin can be ensured as well as a simplified structureof the peripheral circuitry and reduced data write noise can beachieved. Moreover, by sharing the read word line RWL, improvedintegration of the memory array 10 can also be achieved simultaneously.

Tenth Embodiment

Referring to FIG. 75, in the MTJ memory cell according to the tenthembodiment, the access transistor ATR is coupled between the common lineCML and the magnetic tunnel junction MTJ. The read word line RWL iscoupled to the gate of the access transistor ATR. The write bit line WBLextends in the same direction as that of the read word line RWL, and iselectrically coupled to the magnetic tunnel junction MTJ.

In the data write operation, like the write word line WWL, the commonline CML is selectively activated by the write word line driver 30 w. Inthe data read operation, the sense current Is is supplied to the commonline CML.

In the data write operation, in response to turning-ON of the currentcontrol transistor 41-1 to 41-m, the data write current Ip flows throughthe common line CML activated to the selected state (H level), like thewrite word line WWL. In the data read operation, the current controltransistor 41-1 to 41-m is turned OFF, whereby the sense current Isflows through the path formed by the common line CML, magnetic tunneljunction MTJ, access transistor ATR and write bit line WBL (groundvoltage Vss). As a result, a voltage change corresponding to the storagedata of the magnetic tunnel junction MTJ is produced on the common lineCML, as described in connection with FIG. 67.

Thus, as in the ninth embodiment, the common line CML functions as awrite word line WWL in the data write operation and as a read bit lineRBL in the data read operation, whereby the number of wirings can bereduced.

Moreover, the read word line RWL and the common line CML functioning asa write word line in the data write operation extend perpendicularly toeach other. Therefore, the read word line driver 30 r and the write wordline driver 30 w can be independently provided, whereby the same effectsas those of the sixth embodiment can be obtained.

Referring to FIG. 76, in the MTJ memory cell according to the tenthembodiment, the common line CML is provided in the first metal wiringlayer M1 so as to be electrically coupled to the source/drain region 110of the access transistor ATR. The read word line RWL is formed in thesame layer as that of the gate 130 of the access transistor ATR.

The source/drain region 120 is coupled to the magnetic tunnel junctionMTJ through the metal wiring formed in the first metal wiring layer M1,the barrier metal 140, and the metal film 150 formed in the contacthole. The write bit line WBL is provided in the second metal wiringlayer M2 so as to be electrically coupled to the magnetic tunneljunction MTJ.

The common line CML and the magnetic tunnel junction MTJ are coupled toeach other through the access transistor ATR. Therefore, the common lineCML is coupled to the magnetic tunnel junction MTJ only when the accesstransistor ATR is turned ON. As a result, the capacitance of the commonline CML functioning as a read bit line RBL in the data read operationis reduced, whereby the data read operation speed can further beincreased.

Note that, in the MTJ memory cell of the tenth embodiment, the voltageand current waveforms of each wiling in the data read and writeoperations are the same as those of the ninth embodiment. Therefore,detailed description thereof will not be repeated.

In the MTJ memory cell of the tenth embodiment, the common line CMLfunctioning as a write word line WWL is located farther from themagnetic tunnel junction MTJ than is the write bit line WBL. Therefore,in the MTJ memory cell of the tenth embodiment, a relatively large datawrite current must be applied to the common line CML.

Referring to FIG. 77, in the memory array according to the tenthembodiment, the memory cells MC shown in FIG. 75 are arranged in rowsand columns.

The read word lines RWL and the write bit lines WBL extend in the rowdirection. The common lines CML extend in the column direction.

Adjacent memory cells in the row direction share the same common lineCML.

For example, the memory cell group of the first and second memory cellcolumns shares the same common line CML1, and the memory cell group ofthe third and fourth memory cell columns shares the same common lineCML2. In the following memory cell columns as well, the common lines CMLare arranged similarly.

If the data is to be read from or written to a plurality of memory cellsMC of the same common line CML, data collision occurs. Accordingly, thememory cells MC are arranged alternately.

With such a structure, the pitch of the common lines CML in the memoryarray 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Since the structure of the peripheral circuitry for selectivelysupplying the data write current to the common line CML and the writebit line WBL is the same as that of FIG. 69, detailed descriptionthereof will not be repeated.

As described before, in the MTJ memory cell of the tenth embodiment, arelatively large data write current must be applied to the common lineCML. Accordingly, the common line CML is shared between adjacent memorycells so as to ensure the line pitch thereof. As a result, the linewidth, i.e., the cross-sectional area, of the common line CML isassured, so that the current density thereof can be suppressed. Thus,improved reliability of the MRAM device can be achieved. As describedbefore, for the improved operation reliability, it is also effective toselect a material of these wirings in view of electromigrationresistance.

First Modification of Tenth Embodiment

Referring to FIG. 78, in the memory array according to the firstmodification of the tenth embodiment, adjacent memory cells share thesame write bit line WBL. For example, the memory cell group of thesecond and third memory cell rows shares the same write bit line WBL2.In the following memory cell rows as well, the write bit lines WBL arearranged similarly.

In order to conduct the data write operation normally, a plurality ofmemory cells MC must not be present at the intersection of the samecommon line CML and the same write bit line WBL. Accordingly, the commonline CML is provided in every column, and the memory cells MC arearranged alternately.

Since the structure of the peripheral circuitry associated with the dataread and write operations through the common line CML and write bit lineWBL, as well as the memory cell operation in reading and writing thedata are the same as those of the tenth embodiment, detailed descriptionthereof will not be repeated.

With such a structure, the pitch of the write bit lines WBL in thememory array 10 can be widened. As a result, the memory cells MC can beefficiently arranged, whereby improved integration of the memory array10 as well as reduced chip area of the MRAM device can be achieved.

Second Modification of Tenth Embodiment

Referring to FIG. 79, in the memory array according to the secondmodification of the tenth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL. For example, thememory cell group of the first and second memory cell rows shares thesame read word line RWL1. In the following memory cell rows as well, theread word lines RWL are arranged similarly.

Moreover, adjacent memory cells in the column direction share the samewrite bit line WBL. For example, the memory cell group of the second andthird memory cell rows shares the same write bit line WBL2. In thefollowing memory cell rows as well, the write bit lines WBL are arrangedsimilarly.

In order to conduct the data read operation normally, a plurality ofmemory cells MC selected by the same read word line RWL must not besimultaneously coupled to the same common line CML. Accordingly, thecommon line CML is provided in every memory cell column, and the memorycells MC are arranged alternately.

Since the structure is otherwise the same as that of the tenthembodiment, detailed description thereof will not be repeated.

With such a structure, the pitches of the read word lines RWL and writebit lines WBL in the memory array 10 can be widened. As a result, thememory cells MC can be efficiently arranged, whereby improvedintegration of the memory array 10 as well as reduced chip area of theMRAM device can be achieved.

Third Modification of Tenth Embodiment

Referring to FIG. 80, for the memory cells having the structure of thetenth embodiment and arranged in rows and columns, the folded bit linestructure is realized in every set of adjacent two memory cell columns,using corresponding two common lines CML. For example, a data line paircorresponding to a read bit line pair can be formed from the commonlines CML1 and CML2 (/CML1) respectively corresponding to the first andsecond memory cell columns.

Similarly, the folded bit line structure is realized in every set ofadjacent two memory cell rows, using corresponding two write bit linesWBL. For example, a write bit line pair can be formed from the write bitlines WBL1 and WBL2 (/WBL1) respectively corresponding to the first andsecond memory cell rows.

The structure of the peripheral circuitry for conducting row selectionfrom the write bit lines WBL and /WBL of the write bit line pairs andsupplying the data write current ±Iw thereto is the same as that shownin FIG. 72. Therefore, detailed description thereof will not berepeated.

Similarly, the structure of the peripheral circuitry for conductingcolumn selection from the common lines CML and /CML forming the dataline pairs in the data read operation, and supplying the sense currentIs thereto is the same as that shown in FIG. 72. Therefore, detaileddescription thereof will not be repeated.

Accordingly, even when the memory cells according to the tenthembodiment are arranged in rows and columns, the data read and writeoperation margins can be ensured using the folded bit line structure.

Fourth Modification of Tenth Embodiment

In the fourth modification of the tenth embodiment, the write bit lineWBL is shared between adjacent memory cells, in addition to the foldedbit line structure shown in the third modification of the tenthembodiment.

Referring to FIG. 81, in the memory array according to the fourthmodification of the tenth embodiment, adjacent memory cells in thecolumn direction share the same write bit line WBL.

In the read operation, the read word line RWL is activated. In eachcommon line CML functioning as a read bit line RBL, the memory cells areprovided every other read word line RWL. Moreover, the memory cells arearranged alternately between every adjacent common lines CML. Therefore,every set of adjacent two memory cell columns form a data line pair, sothat the data read operation can be conducted based on the folded bitline structure in the same manner as that of the third modification ofthe tenth embodiment.

On the other hand, the data write operation cannot be conducted based onthe folded bit line structure because the write bit line WBL is shared.Accordingly, in the fourth modification of the tenth embodiment, theperipheral circuitry associated with selection of the write bit line WBLis arranged in the same manner as that shown in FIG. 77. Thus, as in thetenth embodiment, the data write operation can be conducted using thedata write circuit 51 b having a simple structure.

Although the data write operation cannot be conducted based on thefolded bit line structure, the pitch of the write word lines WWL in thememory array 10 can be widened. As a result, further improvedintegration of the memory array 10 and thus further reduced chip area ofthe MRAM device can be achieved.

Fifth Modification of Tenth Embodiment

In the fifth modification of the tenth embodiment, the read word lineRWL is shared between adjacent memory cells, in addition to the foldedbit line structure of the third modification of the tenth embodiment.

Referring to FIG. 82, in the memory array according to the fifthmodification of the tenth embodiment, adjacent memory cells in thecolumn direction share the same read word line RWL. The read/writecontrol circuit 60 includes the equalizing transistors 62 and the writebit line voltage control transistors 65, which are arranged in the samemanner as that of the third modification of the tenth embodiment.

In each write bit line WBL, the memory cells are provided every othercommon line CML. Moreover, the memory cells are arranged alternatelybetween every adjacent write bit lines WBL. Therefore, in the data writeoperation, every set of adjacent two memory cell rows can form a writebit line pair. As a result, the data write operation can be conductedbased on the folded bit line structure in the same manner as that of thethird modification of the tenth embodiment, so that the same effects canbe obtained.

On the other hand, in the data read operation, the read word line RWLshared by a plurality of memory cell rows is activated. Therefore, thedata read operation cannot be conducted based on the folded bit linestructure. Accordingly, in the fifth modification of the tenthembodiment, the peripheral circuitry associated with selection of thecommon line CML functioning as a read bit line RBL is arranged in thesame manner as that shown in FIG. 69.

With such a structure, the read operation margin based on the folded bitline structure cannot be ensured, but the pitch of the read word linesRWL in the memory array 10 can be widened, and the data read operationcan be conducted normally. As a result, improved integration of thememory array 10 and thus reduced chip area of the MRAM device can beachieved.

Accordingly, by conducting the data write operation based on the foldedbit line structure using the memory cells of the tenth embodiment, thewrite operation margin can be ensured as well as a simplified structureof the peripheral circuitry and reduced data write noise can beachieved. Moreover, by sharing the read word line RWL, improvedintegration of the memory array 10 can also be achieved simultaneously.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spritand scope of the present invention being limited only by the terms ofthe appended claims.

1-15. (canceled)
 16. A thin film magnetic memory device comprising: amemory array including a plurality of magnetic memory cells; a pluralityof bit lines for reading out memory cell data stored in said magneticmemory cells; a sense amplifier for sensing the memory cell data readout on said bit lines; and a bit line selecting portion provided betweensaid bit lines and said sense amplifier and for selecting a bit linepair, wherein every two of said bit lines form the bit line pair, andthe two bit lines forming the bit line pair are arranged in parallelwith each other, and said bit line selecting portion connects theselected bit line pair to said sense amplifier in a data read.
 17. Thethin film magnetic memory device according to claim 16, furthercomprising a dummy cell for generating a reference level for use in saiddata read, wherein one bit line and the other bit line forming the bitline pair connected to said sense amplifier are further connected to oneof said magnetic memory cells and said dummy cell, respectively.
 18. Thethin film magnetic memory device according to claim 16, furthercomprising a plurality of data lines for writing data to said magneticmemory cells, wherein said data lines are arranged not to form a dataline pair consisting of two data lines parallel and adjacent to eachother.
 19. A thin film magnetic memory device comprising: a memory arrayincluding a plurality of magnetic memory cells; a plurality of bit linesfor reading out memory cell data stored in said magnetic memory cells;and a data output circuit for outputting output data in accordance withthe memory cell data, said data output circuit including a senseamplifier for sensing the memory cell data read out on said bit lines,and a data latch circuit for latching the output of said sense amplifierto generate said output data.
 20. A thin film magnetic memory devicefurther comprising: a memory array including a plurality of magneticmemory cells; a plurality of data write current lines for writing datato said magnetic memory cells; and a current driver for selectivelyconnecting one end side of at least one of said data write current linesto a driving voltage; wherein the other end side of each of said datawrite current lines is connected to a fixed voltage.
 21. A thin filmmagnetic memory device further comprising: a memory array including aplurality of magnetic memory cells; a plurality of data write currentlines for writing data to said magnetic memory cells; and a data writecircuit for supplying a data write current to a selected data writecurrent line of said data write current lines that corresponds to aselected memory cell of said magnetic memory cells, wherein said datawrite circuit guides at least a part of said data write current on saidselected data write current line to at least one of the remainingunselected data write current line of data write current lines, and amagnetic field generated by said selected data write current line and amagnetic field generated by said unselected data write current line actto cancel each other in a region corresponding to at least one of themagnetic memory cells other than said selected memory cells.
 22. Thethin film magnetic memory device according claim 21, further comprisinga current driver for selectively connecting one end side of at least oneof said data write current lines to a driving voltage; wherein the otherend side of each of said data write current lines is connected to afixed voltage.